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 $58.88   12.721%   $66.3701   $66.37   $66.35   $66.40  
  Purchase #2 $18.78   4.812%   $19.6837   $19.68   $19.70   $19.70  
  Purchase #3 $181.47   10.827%   $201.1178   $201.12   $201.10   $201.10  
  Purchase #4 $25.34   9.432%   $27.7301   $27.73   $27.75   $27.70  
  Purchase #5 $212.35   3.731%   $220.2728   $220.27   $220.25   $220.30  
  Purchase #6 $162.94   13.410%   $184.7903   $184.79   $184.80   $184.80  
  Purchase #7 $46.58   10.182%   $51.3228   $51.32   $51.30   $51.30  
  7 purchase totals = $706.34       $771.2876   $771.28   $771.25   $771.30