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 $49.96   13.154%   $56.5317   $56.53   $56.55   $56.50  
  Purchase #2 $140.46   13.246%   $159.0653   $159.07   $159.05   $159.10  
  Purchase #3 $53.64   9.699%   $58.8425   $58.84   $58.85   $58.80  
  Purchase #4 $105.77   11.336%   $117.7601   $117.76   $117.75   $117.80  
  Purchase #5 $209.37   4.141%   $218.04   $218.04   $218.05   $218.00  
  Purchase #6 $206.85   5.172%   $217.5483   $217.55   $217.55   $217.50  
  Purchase #7 $188.76   3.347%   $195.0778   $195.08   $195.10   $195.10  
  7 purchase totals = $954.81       $1,022.8657   $1,022.87   $1,022.90   $1,022.80