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 $137.97   10.433%   $152.3644   $152.36   $152.35   $152.40  
  Purchase #2 $247.90   12.659%   $279.2817   $279.28   $279.30   $279.30  
  Purchase #3 $226.72   11.645%   $253.1215   $253.12   $253.10   $253.10  
  Purchase #4 $74.57   10.228%   $82.197   $82.20   $82.20   $82.20  
  Purchase #5 $207.71   5.659%   $219.4643   $219.46   $219.45   $219.50  
  Purchase #6 $167.27   12.332%   $187.8977   $187.90   $187.90   $187.90  
  Purchase #7 $61.69   12.331%   $69.297   $69.30   $69.30   $69.30  
  7 purchase totals = $1,123.83       $1,243.6236   $1,243.62   $1,243.60   $1,243.70