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 $210.46   7.628%   $226.5139   $226.51   $226.50   $226.50  
  Purchase #2 $33.92   3.207%   $35.0078   $35.01   $35.00   $35.00  
  Purchase #3 $29.77   6.252%   $31.6312   $31.63   $31.65   $31.60  
  Purchase #4 $46.28   4.489%   $48.3575   $48.36   $48.35   $48.40  
  Purchase #5 $52.62   3.701%   $54.5675   $54.57   $54.55   $54.60  
  Purchase #6 $190.44   3.524%   $197.1511   $197.15   $197.15   $197.20  
  Purchase #7 $110.80   8.824%   $120.577   $120.58   $120.60   $120.60  
  7 purchase totals = $674.29       $713.8060   $713.81   $713.80   $713.90