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 $250.94   11.250%   $279.1708   $279.17   $279.15   $279.20  
  Purchase #2 $97.89   13.170%   $110.7821   $110.78   $110.80   $110.80  
  Purchase #3 $32.89   3.739%   $34.1198   $34.12   $34.10   $34.10  
  Purchase #4 $247.43   10.782%   $274.1079   $274.11   $274.10   $274.10  
  Purchase #5 $11.36   12.236%   $12.75   $12.75   $12.75   $12.80  
  Purchase #6 $134.54   3.836%   $139.701   $139.70   $139.70   $139.70  
  Purchase #7 $204.71   6.385%   $217.7807   $217.78   $217.80   $217.80  
  7 purchase totals = $979.76       $1,068.4123   $1,068.41   $1,068.40   $1,068.50