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 $246.87   10.172%   $271.9816   $271.98   $272.00   $272.00  
  Purchase #2 $195.33   7.169%   $209.3332   $209.33   $209.35   $209.30  
  Purchase #3 $240.39   9.746%   $263.8184   $263.82   $263.80   $263.80  
  Purchase #4 $67.69   7.670%   $72.8818   $72.88   $72.90   $72.90  
  Purchase #5 $243.48   11.704%   $271.9769   $271.98   $272.00   $272.00  
  Purchase #6 $19.99   11.591%   $22.307   $22.31   $22.30   $22.30  
  Purchase #7 $196.68   5.595%   $207.6842   $207.68   $207.70   $207.70  
  7 purchase totals = $1,210.43       $1,319.9831   $1,319.98   $1,320.05   $1,320.00