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 $86.59   9.242%   $94.5926   $94.59   $94.60   $94.60  
  Purchase #2 $227.43   9.782%   $249.6772   $249.68   $249.70   $249.70  
  Purchase #3 $121.55   13.594%   $138.0735   $138.07   $138.05   $138.10  
  Purchase #4 $54.26   3.195%   $55.9936   $55.99   $56.00   $56.00  
  Purchase #5 $36.99   12.651%   $41.6696   $41.67   $41.65   $41.70  
  Purchase #6 $66.74   12.677%   $75.2006   $75.20   $75.20   $75.20  
  Purchase #7 $250.59   11.779%   $280.107   $280.11   $280.10   $280.10  
  7 purchase totals = $844.15       $935.3141   $935.31   $935.30   $935.40