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 $205.84   5.762%   $217.7005   $217.70   $217.70   $217.70  
  Purchase #2 $81.77   3.709%   $84.8028   $84.80   $84.80   $84.80  
  Purchase #3 $20.75   4.441%   $21.6715   $21.67   $21.65   $21.70  
  Purchase #4 $82.39   11.841%   $92.1458   $92.15   $92.15   $92.10  
  Purchase #5 $95.75   9.261%   $104.6174   $104.62   $104.60   $104.60  
  Purchase #6 $104.91   3.330%   $108.4035   $108.40   $108.40   $108.40  
  Purchase #7 $81.85   4.364%   $85.4219   $85.42   $85.40   $85.40  
  7 purchase totals = $673.26       $714.7634   $714.76   $714.70   $714.70