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 $204.62   11.280%   $227.7011   $227.70   $227.70   $227.70  
  Purchase #2 $53.96   13.312%   $61.1432   $61.14   $61.15   $61.10  
  Purchase #3 $208.33   6.834%   $222.5673   $222.57   $222.55   $222.60  
  Purchase #4 $35.74   3.397%   $36.9541   $36.95   $36.95   $37.00  
  Purchase #5 $237.76   9.497%   $260.3401   $260.34   $260.35   $260.30  
  Purchase #6 $183.61   4.290%   $191.4869   $191.49   $191.50   $191.50  
  Purchase #7 $30.55   10.475%   $33.7501   $33.75   $33.75   $33.80  
  7 purchase totals = $954.57       $1,033.9428   $1,033.94   $1,033.95   $1,034.00