Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $191.52   13.804%   $217.9574   $217.96   $217.95   $218.00  
  Purchase #2 $246.32   6.407%   $262.1017   $262.10   $262.10   $262.10  
  Purchase #3 $241.27   5.568%   $254.7039   $254.70   $254.70   $254.70  
  Purchase #4 $209.46   6.812%   $223.7284   $223.73   $223.75   $223.70  
  Purchase #5 $128.93   13.820%   $146.7481   $146.75   $146.75   $146.70  
  Purchase #6 $203.90   11.608%   $227.5687   $227.57   $227.55   $227.60  
  Purchase #7 $246.28   7.526%   $264.815   $264.82   $264.80   $264.80  
  7 purchase totals = $1,467.68       $1,597.6232   $1,597.63   $1,597.60   $1,597.60