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 $22.45   6.711%   $23.9566   $23.96   $23.95   $24.00  
  Purchase #2 $58.69   10.694%   $64.9663   $64.97   $64.95   $65.00  
  Purchase #3 $193.34   4.316%   $201.6846   $201.68   $201.70   $201.70  
  Purchase #4 $51.34   12.446%   $57.7298   $57.73   $57.75   $57.70  
  Purchase #5 $116.34   7.630%   $125.2167   $125.22   $125.20   $125.20  
  Purchase #6 $94.57   10.799%   $104.7826   $104.78   $104.80   $104.80  
  Purchase #7 $228.66   11.601%   $255.1868   $255.19   $255.20   $255.20  
  7 purchase totals = $765.39       $833.5234   $833.53   $833.55   $833.60