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 $21.30   3.611%   $22.0691   $22.07   $22.05   $22.10  
  Purchase #2 $34.44   7.535%   $37.0351   $37.04   $37.05   $37.00  
  Purchase #3 $245.47   5.596%   $259.2065   $259.21   $259.20   $259.20  
  Purchase #4 $23.83   5.503%   $25.1414   $25.14   $25.15   $25.10  
  Purchase #5 $235.67   4.418%   $246.0819   $246.08   $246.10   $246.10  
  Purchase #6 $32.87   11.258%   $36.5705   $36.57   $36.55   $36.60  
  Purchase #7 $94.42   13.778%   $107.4292   $107.43   $107.45   $107.40  
  7 purchase totals = $688.00       $733.5337   $733.54   $733.55   $733.50