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 $42.66   7.462%   $45.8433   $45.84   $45.85   $45.80  
  Purchase #2 $24.50   3.673%   $25.3999   $25.40   $25.40   $25.40  
  Purchase #3 $106.70   11.497%   $118.9673   $118.97   $118.95   $119.00  
  Purchase #4 $242.91   6.523%   $258.755   $258.76   $258.75   $258.80  
  Purchase #5 $226.39   4.258%   $236.0297   $236.03   $236.05   $236.00  
  Purchase #6 $55.97   13.586%   $63.5741   $63.57   $63.55   $63.60  
  Purchase #7 $246.51   11.517%   $274.9006   $274.90   $274.90   $274.90  
  7 purchase totals = $945.64       $1,023.4699   $1,023.47   $1,023.45   $1,023.50