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 $49.68   10.827%   $55.0589   $55.06   $55.05   $55.10  
  Purchase #2 $221.38   4.786%   $231.9752   $231.98   $232.00   $232.00  
  Purchase #3 $29.94   7.821%   $32.2816   $32.28   $32.30   $32.30  
  Purchase #4 $146.65   9.638%   $160.7841   $160.78   $160.80   $160.80  
  Purchase #5 $25.69   4.492%   $26.844   $26.84   $26.85   $26.80  
  Purchase #6 $109.73   4.409%   $114.568   $114.57   $114.55   $114.60  
  Purchase #7 $129.48   7.824%   $139.6105   $139.61   $139.60   $139.60  
  7 purchase totals = $712.55       $761.1223   $761.12   $761.15   $761.20