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 $206.61   4.121%   $215.1244   $215.12   $215.10   $215.10  
  Purchase #2 $209.62   5.226%   $220.5747   $220.57   $220.55   $220.60  
  Purchase #3 $80.82   9.648%   $88.6175   $88.62   $88.60   $88.60  
  Purchase #4 $246.99   9.796%   $271.1851   $271.19   $271.20   $271.20  
  Purchase #5 $237.37   8.477%   $257.4919   $257.49   $257.50   $257.50  
  Purchase #6 $50.88   4.630%   $53.2357   $53.24   $53.25   $53.20  
  Purchase #7 $222.27   8.601%   $241.3874   $241.39   $241.40   $241.40  
  7 purchase totals = $1,254.56       $1,347.6167   $1,347.62   $1,347.60   $1,347.60