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 $176.98   12.779%   $199.5963   $199.60   $199.60   $199.60  
  Purchase #2 $124.94   11.856%   $139.7529   $139.75   $139.75   $139.80  
  Purchase #3 $104.40   13.375%   $118.3635   $118.36   $118.35   $118.40  
  Purchase #4 $126.31   3.153%   $130.2926   $130.29   $130.30   $130.30  
  Purchase #5 $133.62   10.483%   $147.6274   $147.63   $147.65   $147.60  
  Purchase #6 $110.31   10.476%   $121.8661   $121.87   $121.85   $121.90  
  Purchase #7 $82.79   13.573%   $94.0271   $94.03   $94.05   $94.00  
  7 purchase totals = $859.35       $951.5259   $951.53   $951.55   $951.60