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 $56.33   6.609%   $60.0528   $60.05   $60.05   $60.10  
  Purchase #2 $119.58   5.650%   $126.3363   $126.34   $126.35   $126.30  
  Purchase #3 $82.50   12.494%   $92.8076   $92.81   $92.80   $92.80  
  Purchase #4 $250.26   8.858%   $272.428   $272.43   $272.45   $272.40  
  Purchase #5 $148.75   7.167%   $159.4109   $159.41   $159.40   $159.40  
  Purchase #6 $63.75   12.776%   $71.8947   $71.89   $71.90   $71.90  
  Purchase #7 $238.59   9.833%   $262.0506   $262.05   $262.05   $262.10  
  7 purchase totals = $959.76       $1,044.9809   $1,044.98   $1,045.00   $1,045.00