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 $22.56   10.601%   $24.9516   $24.95   $24.95   $25.00  
  Purchase #2 $249.89   9.431%   $273.4571   $273.46   $273.45   $273.50  
  Purchase #3 $89.48   11.395%   $99.6762   $99.68   $99.70   $99.70  
  Purchase #4 $30.25   11.831%   $33.8289   $33.83   $33.85   $33.80  
  Purchase #5 $218.33   8.628%   $237.1675   $237.17   $237.15   $237.20  
  Purchase #6 $121.55   8.871%   $132.3327   $132.33   $132.35   $132.30  
  Purchase #7 $145.45   13.276%   $164.7599   $164.76   $164.75   $164.80  
  7 purchase totals = $877.51       $966.1739   $966.18   $966.20   $966.30