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 $86.96   9.187%   $94.949   $94.95   $94.95   $94.90  
  Purchase #2 $76.39   3.280%   $78.8956   $78.90   $78.90   $78.90  
  Purchase #3 $180.67   12.324%   $202.9358   $202.94   $202.95   $202.90  
  Purchase #4 $62.37   9.776%   $68.4673   $68.47   $68.45   $68.50  
  Purchase #5 $214.41   7.368%   $230.2077   $230.21   $230.20   $230.20  
  Purchase #6 $187.70   8.143%   $202.9844   $202.98   $203.00   $203.00  
  Purchase #7 $117.29   11.494%   $130.7713   $130.77   $130.75   $130.80  
  7 purchase totals = $925.79       $1,009.2111   $1,009.22   $1,009.20   $1,009.20