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 $134.65   12.631%   $151.6576   $151.66   $151.65   $151.70  
  Purchase #2 $187.93   10.606%   $207.8619   $207.86   $207.85   $207.90  
  Purchase #3 $152.59   4.453%   $159.3848   $159.38   $159.40   $159.40  
  Purchase #4 $182.70   8.781%   $198.7429   $198.74   $198.75   $198.70  
  Purchase #5 $43.90   5.492%   $46.311   $46.31   $46.30   $46.30  
  Purchase #6 $90.50   7.334%   $97.1373   $97.14   $97.15   $97.10  
  Purchase #7 $154.77   10.692%   $171.318   $171.32   $171.30   $171.30  
  7 purchase totals = $947.04       $1,032.4135   $1,032.41   $1,032.40   $1,032.40