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 $104.56   8.646%   $113.6003   $113.60   $113.60   $113.60  
  Purchase #2 $141.61   9.773%   $155.4495   $155.45   $155.45   $155.40  
  Purchase #3 $7.65   12.341%   $8.5941   $8.59   $8.60   $8.60  
  Purchase #4 $98.58   10.869%   $109.2947   $109.29   $109.30   $109.30  
  Purchase #5 $163.39   11.353%   $181.9397   $181.94   $181.95   $181.90  
  Purchase #6 $58.31   13.307%   $66.0693   $66.07   $66.05   $66.10  
  Purchase #7 $130.90   4.329%   $136.5667   $136.57   $136.55   $136.60  
  7 purchase totals = $705.00       $771.5143   $771.51   $771.50   $771.50