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 $62.46   8.411%   $67.7135   $67.71   $67.70   $67.70  
  Purchase #2 $90.93   13.262%   $102.9891   $102.99   $103.00   $103.00  
  Purchase #3 $133.62   6.353%   $142.1089   $142.11   $142.10   $142.10  
  Purchase #4 $86.61   10.554%   $95.7508   $95.75   $95.75   $95.80  
  Purchase #5 $245.60   5.425%   $258.9238   $258.92   $258.90   $258.90  
  Purchase #6 $150.33   8.621%   $163.2899   $163.29   $163.30   $163.30  
  Purchase #7 $168.98   13.555%   $191.8852   $191.89   $191.90   $191.90  
  7 purchase totals = $938.53       $1,022.6612   $1,022.66   $1,022.65   $1,022.70