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 $170.26   7.462%   $182.9648   $182.96   $182.95   $183.00  
  Purchase #2 $198.93   12.242%   $223.283   $223.28   $223.30   $223.30  
  Purchase #3 $59.49   7.629%   $64.0285   $64.03   $64.05   $64.00  
  Purchase #4 $146.34   9.298%   $159.9467   $159.95   $159.95   $159.90  
  Purchase #5 $223.55   6.517%   $238.1188   $238.12   $238.10   $238.10  
  Purchase #6 $54.46   6.583%   $58.0451   $58.05   $58.05   $58.00  
  Purchase #7 $111.48   6.211%   $118.404   $118.40   $118.40   $118.40  
  7 purchase totals = $964.51       $1,044.7909   $1,044.79   $1,044.80   $1,044.70