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 $56.93   4.265%   $59.3581   $59.36   $59.35   $59.40  
  Purchase #2 $178.79   4.309%   $186.4941   $186.49   $186.50   $186.50  
  Purchase #3 $67.89   7.507%   $72.9865   $72.99   $73.00   $73.00  
  Purchase #4 $210.95   7.356%   $226.4675   $226.47   $226.45   $226.50  
  Purchase #5 $226.42   4.824%   $237.3425   $237.34   $237.35   $237.30  
  Purchase #6 $216.94   11.152%   $241.1331   $241.13   $241.15   $241.10  
  Purchase #7 $72.75   12.670%   $81.9674   $81.97   $81.95   $82.00  
  7 purchase totals = $1,030.67       $1,105.7492   $1,105.75   $1,105.75   $1,105.80