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 $176.31   9.832%   $193.6448   $193.64   $193.65   $193.60  
  Purchase #2 $124.68   11.136%   $138.5644   $138.56   $138.55   $138.60  
  Purchase #3 $140.49   4.549%   $146.8809   $146.88   $146.90   $146.90  
  Purchase #4 $159.59   8.643%   $173.3834   $173.38   $173.40   $173.40  
  Purchase #5 $190.30   8.739%   $206.9303   $206.93   $206.95   $206.90  
  Purchase #6 $29.71   11.615%   $33.1608   $33.16   $33.15   $33.20  
  Purchase #7 $140.83   7.342%   $151.1697   $151.17   $151.15   $151.20  
  7 purchase totals = $961.91       $1,043.7343   $1,043.72   $1,043.75   $1,043.80