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 $189.31   10.318%   $208.843   $208.84   $208.85   $208.80  
  Purchase #2 $111.47   12.790%   $125.727   $125.73   $125.75   $125.70  
  Purchase #3 $201.55   7.612%   $216.892   $216.89   $216.90   $216.90  
  Purchase #4 $160.40   11.713%   $179.1877   $179.19   $179.20   $179.20  
  Purchase #5 $170.83   6.279%   $181.5564   $181.56   $181.55   $181.60  
  Purchase #6 $107.92   4.154%   $112.403   $112.40   $112.40   $112.40  
  Purchase #7 $243.64   7.499%   $261.9106   $261.91   $261.90   $261.90  
  7 purchase totals = $1,185.12       $1,286.5197   $1,286.52   $1,286.55   $1,286.50