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 $241.54   3.753%   $250.605   $250.61   $250.60   $250.60  
  Purchase #2 $232.68   12.164%   $260.9832   $260.98   $261.00   $261.00  
  Purchase #3 $5.38   4.771%   $5.6367   $5.64   $5.65   $5.60  
  Purchase #4 $207.81   8.784%   $226.064   $226.06   $226.05   $226.10  
  Purchase #5 $187.61   3.763%   $194.6698   $194.67   $194.65   $194.70  
  Purchase #6 $224.55   8.593%   $243.8456   $243.85   $243.85   $243.80  
  Purchase #7 $35.74   7.398%   $38.384   $38.38   $38.40   $38.40  
  7 purchase totals = $1,135.31       $1,220.1883   $1,220.19   $1,220.20   $1,220.20