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 $94.54   3.384%   $97.7392   $97.74   $97.75   $97.70  
  Purchase #2 $65.87   4.231%   $68.657   $68.66   $68.65   $68.70  
  Purchase #3 $141.38   13.631%   $160.6515   $160.65   $160.65   $160.70  
  Purchase #4 $249.46   13.282%   $282.5933   $282.59   $282.60   $282.60  
  Purchase #5 $184.87   3.106%   $190.6121   $190.61   $190.60   $190.60  
  Purchase #6 $88.49   12.339%   $99.4088   $99.41   $99.40   $99.40  
  Purchase #7 $118.98   6.523%   $126.7411   $126.74   $126.75   $126.70  
  7 purchase totals = $943.59       $1,026.4030   $1,026.40   $1,026.40   $1,026.40