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 $59.51   11.417%   $66.3043   $66.30   $66.30   $66.30  
  Purchase #2 $199.25   9.127%   $217.4355   $217.44   $217.45   $217.40  
  Purchase #3 $75.84   4.482%   $79.2391   $79.24   $79.25   $79.20  
  Purchase #4 $101.93   13.127%   $115.3104   $115.31   $115.30   $115.30  
  Purchase #5 $181.82   4.712%   $190.3874   $190.39   $190.40   $190.40  
  Purchase #6 $126.41   10.513%   $139.6995   $139.70   $139.70   $139.70  
  Purchase #7 $172.54   11.123%   $191.7316   $191.73   $191.75   $191.70  
  7 purchase totals = $917.30       $1,000.1078   $1,000.11   $1,000.15   $1,000.00