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 $62.51   13.156%   $70.7338   $70.73   $70.75   $70.70  
  Purchase #2 $182.94   10.106%   $201.4279   $201.43   $201.45   $201.40  
  Purchase #3 $194.67   7.841%   $209.9341   $209.93   $209.95   $209.90  
  Purchase #4 $37.64   9.329%   $41.1514   $41.15   $41.15   $41.20  
  Purchase #5 $191.68   4.706%   $200.7005   $200.70   $200.70   $200.70  
  Purchase #6 $249.95   8.690%   $271.6707   $271.67   $271.65   $271.70  
  Purchase #7 $226.63   10.625%   $250.7094   $250.71   $250.70   $250.70  
  7 purchase totals = $1,146.02       $1,246.3278   $1,246.32   $1,246.35   $1,246.30