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 $194.93   11.622%   $217.5848   $217.58   $217.60   $217.60  
  Purchase #2 $59.92   9.601%   $65.6729   $65.67   $65.65   $65.70  
  Purchase #3 $234.89   6.464%   $250.0733   $250.07   $250.05   $250.10  
  Purchase #4 $241.34   10.113%   $265.7467   $265.75   $265.75   $265.70  
  Purchase #5 $58.70   7.540%   $63.126   $63.13   $63.15   $63.10  
  Purchase #6 $165.46   5.834%   $175.1129   $175.11   $175.10   $175.10  
  Purchase #7 $139.43   7.668%   $150.1215   $150.12   $150.10   $150.10  
  7 purchase totals = $1,094.67       $1,187.4381   $1,187.43   $1,187.40   $1,187.40