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 $91.95   11.104%   $102.1601   $102.16   $102.15   $102.20  
  Purchase #2 $125.28   12.657%   $141.1367   $141.14   $141.15   $141.10  
  Purchase #3 $162.58   9.422%   $177.8983   $177.90   $177.90   $177.90  
  Purchase #4 $248.41   4.431%   $259.417   $259.42   $259.40   $259.40  
  Purchase #5 $100.53   3.873%   $104.4235   $104.42   $104.40   $104.40  
  Purchase #6 $118.48   11.477%   $132.0779   $132.08   $132.10   $132.10  
  Purchase #7 $104.90   13.129%   $118.6723   $118.67   $118.65   $118.70  
  7 purchase totals = $952.13       $1,035.7858   $1,035.79   $1,035.75   $1,035.80