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 $217.82   13.159%   $246.4829   $246.48   $246.50   $246.50  
  Purchase #2 $55.88   8.382%   $60.5639   $60.56   $60.55   $60.60  
  Purchase #3 $128.26   10.416%   $141.6196   $141.62   $141.60   $141.60  
  Purchase #4 $223.89   12.236%   $251.2852   $251.29   $251.30   $251.30  
  Purchase #5 $217.62   13.348%   $246.6679   $246.67   $246.65   $246.70  
  Purchase #6 $15.77   13.704%   $17.9311   $17.93   $17.95   $17.90  
  Purchase #7 $233.83   12.746%   $263.634   $263.63   $263.65   $263.60  
  7 purchase totals = $1,093.07       $1,228.1846   $1,228.18   $1,228.20   $1,228.20