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 $220.46   11.351%   $245.4844   $245.48   $245.50   $245.50  
  Purchase #2 $131.72   13.122%   $149.0043   $149.00   $149.00   $149.00  
  Purchase #3 $119.90   11.446%   $133.6238   $133.62   $133.60   $133.60  
  Purchase #4 $107.54   5.546%   $113.5042   $113.50   $113.50   $113.50  
  Purchase #5 $29.57   11.620%   $33.006   $33.01   $33.00   $33.00  
  Purchase #6 $43.49   6.404%   $46.2751   $46.28   $46.30   $46.30  
  Purchase #7 $216.64   13.566%   $246.0294   $246.03   $246.05   $246.00  
  7 purchase totals = $869.32       $966.9272   $966.92   $966.95   $966.90