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 $216.46   12.435%   $243.3768   $243.38   $243.40   $243.40  
  Purchase #2 $162.72   7.569%   $175.0363   $175.04   $175.05   $175.00  
  Purchase #3 $36.29   5.134%   $38.1531   $38.15   $38.15   $38.20  
  Purchase #4 $102.60   10.309%   $113.177   $113.18   $113.20   $113.20  
  Purchase #5 $204.90   6.122%   $217.444   $217.44   $217.45   $217.40  
  Purchase #6 $101.46   3.352%   $104.8609   $104.86   $104.85   $104.90  
  Purchase #7 $93.73   9.488%   $102.6231   $102.62   $102.60   $102.60  
  7 purchase totals = $918.16       $994.6712   $994.67   $994.70   $994.70