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 $228.88   10.730%   $253.4388   $253.44   $253.45   $253.40  
  Purchase #2 $85.33   9.847%   $93.7324   $93.73   $93.75   $93.70  
  Purchase #3 $163.48   3.598%   $169.362   $169.36   $169.35   $169.40  
  Purchase #4 $213.47   11.112%   $237.1908   $237.19   $237.20   $237.20  
  Purchase #5 $64.77   8.371%   $70.1919   $70.19   $70.20   $70.20  
  Purchase #6 $223.74   10.159%   $246.4697   $246.47   $246.45   $246.50  
  Purchase #7 $100.77   11.687%   $112.547   $112.55   $112.55   $112.50  
  7 purchase totals = $1,080.44       $1,182.9326   $1,182.93   $1,182.95   $1,182.90