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 $234.37   12.139%   $262.8202   $262.82   $262.80   $262.80  
  Purchase #2 $93.32   11.226%   $103.7961   $103.80   $103.80   $103.80  
  Purchase #3 $164.34   6.286%   $174.6704   $174.67   $174.65   $174.70  
  Purchase #4 $44.85   9.195%   $48.974   $48.97   $48.95   $49.00  
  Purchase #5 $44.88   9.543%   $49.1629   $49.16   $49.15   $49.20  
  Purchase #6 $36.85   12.741%   $41.5451   $41.55   $41.55   $41.50  
  Purchase #7 $89.97   12.443%   $101.165   $101.17   $101.15   $101.20  
  7 purchase totals = $708.58       $782.1337   $782.14   $782.05   $782.20