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 $193.82   4.604%   $202.7435   $202.74   $202.75   $202.70  
  Purchase #2 $80.69   8.263%   $87.3574   $87.36   $87.35   $87.40  
  Purchase #3 $10.45   5.688%   $11.0444   $11.04   $11.05   $11.00  
  Purchase #4 $68.34   7.211%   $73.268   $73.27   $73.25   $73.30  
  Purchase #5 $195.68   4.395%   $204.2801   $204.28   $204.30   $204.30  
  Purchase #6 $203.72   3.621%   $211.0967   $211.10   $211.10   $211.10  
  Purchase #7 $13.68   9.512%   $14.9812   $14.98   $15.00   $15.00  
  7 purchase totals = $766.38       $804.7713   $804.77   $804.80   $804.80