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 $141.81   6.308%   $150.7554   $150.76   $150.75   $150.80  
  Purchase #2 $234.34   10.177%   $258.1888   $258.19   $258.20   $258.20  
  Purchase #3 $99.79   8.312%   $108.0845   $108.08   $108.10   $108.10  
  Purchase #4 $123.37   10.580%   $136.4225   $136.42   $136.40   $136.40  
  Purchase #5 $110.64   9.425%   $121.0678   $121.07   $121.05   $121.10  
  Purchase #6 $33.76   6.593%   $35.9858   $35.99   $36.00   $36.00  
  Purchase #7 $207.46   3.150%   $213.995   $214.00   $214.00   $214.00  
  7 purchase totals = $951.17       $1,024.4998   $1,024.51   $1,024.50   $1,024.60