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 $35.72   6.452%   $38.0247   $38.02   $38.00   $38.00  
  Purchase #2 $207.64   10.566%   $229.5792   $229.58   $229.60   $229.60  
  Purchase #3 $60.86   11.645%   $67.9471   $67.95   $67.95   $67.90  
  Purchase #4 $123.56   10.784%   $136.8847   $136.88   $136.90   $136.90  
  Purchase #5 $171.71   9.433%   $187.9074   $187.91   $187.90   $187.90  
  Purchase #6 $182.80   8.358%   $198.0784   $198.08   $198.10   $198.10  
  Purchase #7 $83.41   5.444%   $87.9508   $87.95   $87.95   $88.00  
  7 purchase totals = $865.70       $946.3723   $946.37   $946.40   $946.40