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 $12.85   9.750%   $14.1029   $14.10   $14.10   $14.10  
  Purchase #2 $201.36   7.815%   $217.0963   $217.10   $217.10   $217.10  
  Purchase #3 $152.28   11.424%   $169.6765   $169.68   $169.70   $169.70  
  Purchase #4 $101.60   11.290%   $113.0706   $113.07   $113.05   $113.10  
  Purchase #5 $174.67   9.795%   $191.7789   $191.78   $191.80   $191.80  
  Purchase #6 $231.98   7.523%   $249.4319   $249.43   $249.45   $249.40  
  Purchase #7 $97.71   3.166%   $100.8035   $100.80   $100.80   $100.80  
  7 purchase totals = $972.45       $1,055.9606   $1,055.96   $1,056.00   $1,056.00