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 $228.79   11.228%   $254.4785   $254.48   $254.50   $254.50  
  Purchase #2 $201.79   7.812%   $217.5538   $217.55   $217.55   $217.60  
  Purchase #3 $210.30   5.492%   $221.8497   $221.85   $221.85   $221.80  
  Purchase #4 $67.72   8.507%   $73.4809   $73.48   $73.50   $73.50  
  Purchase #5 $115.25   7.664%   $124.0828   $124.08   $124.10   $124.10  
  Purchase #6 $34.44   6.268%   $36.5987   $36.60   $36.60   $36.60  
  Purchase #7 $203.29   9.681%   $222.9705   $222.97   $222.95   $223.00  
  7 purchase totals = $1,061.58       $1,151.0149   $1,151.01   $1,151.05   $1,151.10