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 $204.98   13.536%   $232.7261   $232.73   $232.75   $232.70  
  Purchase #2 $77.95   9.413%   $85.2874   $85.29   $85.30   $85.30  
  Purchase #3 $90.38   4.575%   $94.5149   $94.51   $94.50   $94.50  
  Purchase #4 $110.68   12.681%   $124.7153   $124.72   $124.70   $124.70  
  Purchase #5 $213.25   11.516%   $237.8079   $237.81   $237.80   $237.80  
  Purchase #6 $55.73   4.179%   $58.059   $58.06   $58.05   $58.10  
  Purchase #7 $245.86   11.294%   $273.6274   $273.63   $273.65   $273.60  
  7 purchase totals = $998.83       $1,106.7380   $1,106.75   $1,106.75   $1,106.70