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 $131.64   11.138%   $146.3021   $146.30   $146.30   $146.30  
  Purchase #2 $144.45   8.870%   $157.2627   $157.26   $157.25   $157.30  
  Purchase #3 $178.28   5.192%   $187.5363   $187.54   $187.55   $187.50  
  Purchase #4 $207.80   7.691%   $223.7819   $223.78   $223.80   $223.80  
  Purchase #5 $203.45   8.569%   $220.8836   $220.88   $220.90   $220.90  
  Purchase #6 $68.26   12.310%   $76.6628   $76.66   $76.65   $76.70  
  Purchase #7 $151.36   12.208%   $169.838   $169.84   $169.85   $169.80  
  7 purchase totals = $1,085.24       $1,182.2674   $1,182.26   $1,182.30   $1,182.30