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 $92.60   11.260%   $103.0268   $103.03   $103.05   $103.00  
  Purchase #2 $62.99   9.794%   $69.1592   $69.16   $69.15   $69.20  
  Purchase #3 $53.85   9.466%   $58.9474   $58.95   $58.95   $58.90  
  Purchase #4 $212.83   6.797%   $227.2961   $227.30   $227.30   $227.30  
  Purchase #5 $61.27   3.695%   $63.5339   $63.53   $63.55   $63.50  
  Purchase #6 $103.56   7.760%   $111.5963   $111.60   $111.60   $111.60  
  Purchase #7 $231.46   12.592%   $260.6054   $260.61   $260.60   $260.60  
  7 purchase totals = $818.56       $894.1651   $894.18   $894.20   $894.10