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 $84.83   13.147%   $95.9826   $95.98   $96.00   $96.00  
  Purchase #2 $132.32   5.335%   $139.3793   $139.38   $139.40   $139.40  
  Purchase #3 $44.91   10.537%   $49.6422   $49.64   $49.65   $49.60  
  Purchase #4 $8.80   11.580%   $9.819   $9.82   $9.80   $9.80  
  Purchase #5 $239.60   6.821%   $255.9431   $255.94   $255.95   $255.90  
  Purchase #6 $141.41   6.503%   $150.6059   $150.61   $150.60   $150.60  
  Purchase #7 $248.38   5.270%   $261.4696   $261.47   $261.45   $261.50  
  7 purchase totals = $900.25       $962.8417   $962.84   $962.85   $962.80