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 $204.58   3.524%   $211.7894   $211.79   $211.80   $211.80  
  Purchase #2 $63.66   9.767%   $69.8777   $69.88   $69.90   $69.90  
  Purchase #3 $133.81   6.312%   $142.2561   $142.26   $142.25   $142.30  
  Purchase #4 $42.44   3.779%   $44.0438   $44.04   $44.05   $44.00  
  Purchase #5 $59.82   7.588%   $64.3591   $64.36   $64.35   $64.40  
  Purchase #6 $5.95   6.614%   $6.3435   $6.34   $6.35   $6.30  
  Purchase #7 $235.42   8.510%   $255.4542   $255.45   $255.45   $255.50  
  7 purchase totals = $745.68       $794.1238   $794.12   $794.15   $794.20