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 $107.67   7.756%   $116.0209   $116.02   $116.00   $116.00  
  Purchase #2 $92.79   10.817%   $102.8271   $102.83   $102.85   $102.80  
  Purchase #3 $203.27   6.522%   $216.5273   $216.53   $216.55   $216.50  
  Purchase #4 $220.98   7.160%   $236.8022   $236.80   $236.80   $236.80  
  Purchase #5 $110.87   10.447%   $122.4526   $122.45   $122.45   $122.50  
  Purchase #6 $13.75   3.447%   $14.224   $14.22   $14.20   $14.20  
  Purchase #7 $127.48   4.395%   $133.0827   $133.08   $133.10   $133.10  
  7 purchase totals = $876.81       $941.9368   $941.93   $941.95   $941.90