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 $30.64   6.598%   $32.6616   $32.66   $32.65   $32.70  
  Purchase #2 $21.98   13.180%   $24.877   $24.88   $24.90   $24.90  
  Purchase #3 $178.37   4.836%   $186.996   $187.00   $187.00   $187.00  
  Purchase #4 $183.70   12.472%   $206.6111   $206.61   $206.60   $206.60  
  Purchase #5 $186.75   10.412%   $206.1944   $206.19   $206.20   $206.20  
  Purchase #6 $139.86   5.226%   $147.1691   $147.17   $147.15   $147.20  
  Purchase #7 $197.63   6.451%   $210.3791   $210.38   $210.40   $210.40  
  7 purchase totals = $938.93       $1,014.8883   $1,014.89   $1,014.90   $1,015.00