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 $227.86   7.218%   $244.3069   $244.31   $244.30   $244.30  
  Purchase #2 $68.99   9.727%   $75.7007   $75.70   $75.70   $75.70  
  Purchase #3 $68.38   5.472%   $72.1218   $72.12   $72.10   $72.10  
  Purchase #4 $234.70   6.386%   $249.6879   $249.69   $249.70   $249.70  
  Purchase #5 $167.25   6.686%   $178.4323   $178.43   $178.45   $178.40  
  Purchase #6 $160.50   5.366%   $169.1124   $169.11   $169.10   $169.10  
  Purchase #7 $49.34   13.512%   $56.0068   $56.01   $56.00   $56.00  
  7 purchase totals = $977.02       $1,045.3688   $1,045.37   $1,045.35   $1,045.30