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 $191.94   4.333%   $200.2568   $200.26   $200.25   $200.30  
  Purchase #2 $44.50   3.807%   $46.1941   $46.19   $46.20   $46.20  
  Purchase #3 $243.48   11.170%   $270.6767   $270.68   $270.70   $270.70  
  Purchase #4 $215.62   3.316%   $222.77   $222.77   $222.75   $222.80  
  Purchase #5 $192.46   5.583%   $203.205   $203.21   $203.20   $203.20  
  Purchase #6 $54.61   6.114%   $57.9489   $57.95   $57.95   $57.90  
  Purchase #7 $148.33   6.390%   $157.8083   $157.81   $157.80   $157.80  
  7 purchase totals = $1,090.94       $1,158.8598   $1,158.87   $1,158.85   $1,158.90