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 $144.34   3.548%   $149.4612   $149.46   $149.45   $149.50  
  Purchase #2 $248.90   9.489%   $272.5181   $272.52   $272.50   $272.50  
  Purchase #3 $153.43   9.826%   $168.506   $168.51   $168.50   $168.50  
  Purchase #4 $238.39   13.234%   $269.9385   $269.94   $269.95   $269.90  
  Purchase #5 $24.97   5.415%   $26.3221   $26.32   $26.30   $26.30  
  Purchase #6 $166.78   12.226%   $187.1705   $187.17   $187.15   $187.20  
  Purchase #7 $109.28   13.116%   $123.6132   $123.61   $123.60   $123.60  
  7 purchase totals = $1,086.09       $1,197.5296   $1,197.53   $1,197.45   $1,197.50