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 $244.68   8.132%   $264.5774   $264.58   $264.60   $264.60  
  Purchase #2 $40.41   9.599%   $44.289   $44.29   $44.30   $44.30  
  Purchase #3 $171.57   11.198%   $190.7824   $190.78   $190.80   $190.80  
  Purchase #4 $55.47   3.250%   $57.2728   $57.27   $57.25   $57.30  
  Purchase #5 $160.88   6.368%   $171.1248   $171.12   $171.10   $171.10  
  Purchase #6 $127.31   6.422%   $135.4858   $135.49   $135.50   $135.50  
  Purchase #7 $84.63   6.770%   $90.3595   $90.36   $90.35   $90.40  
  7 purchase totals = $884.95       $953.8917   $953.89   $953.90   $954.00