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 $83.65   11.219%   $93.0347   $93.03   $93.05   $93.00  
  Purchase #2 $106.93   13.801%   $121.6874   $121.69   $121.70   $121.70  
  Purchase #3 $8.81   11.474%   $9.8209   $9.82   $9.80   $9.80  
  Purchase #4 $163.43   4.592%   $170.9347   $170.93   $170.95   $170.90  
  Purchase #5 $130.49   10.674%   $144.4185   $144.42   $144.40   $144.40  
  Purchase #6 $216.41   12.252%   $242.9246   $242.92   $242.90   $242.90  
  Purchase #7 $244.54   8.617%   $265.612   $265.61   $265.60   $265.60  
  7 purchase totals = $954.26       $1,048.4328   $1,048.42   $1,048.40   $1,048.30