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 $55.71   8.303%   $60.3356   $60.34   $60.35   $60.30  
  Purchase #2 $166.82   12.742%   $188.0762   $188.08   $188.10   $188.10  
  Purchase #3 $220.46   3.170%   $227.4486   $227.45   $227.45   $227.40  
  Purchase #4 $213.55   11.303%   $237.6876   $237.69   $237.70   $237.70  
  Purchase #5 $81.58   11.758%   $91.1722   $91.17   $91.15   $91.20  
  Purchase #6 $191.35   10.161%   $210.7931   $210.79   $210.80   $210.80  
  Purchase #7 $233.96   5.490%   $246.8044   $246.80   $246.80   $246.80  
  7 purchase totals = $1,163.43       $1,262.3177   $1,262.32   $1,262.35   $1,262.30