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 $84.68   11.765%   $94.6426   $94.64   $94.65   $94.60  
  Purchase #2 $134.67   10.325%   $148.5747   $148.57   $148.55   $148.60  
  Purchase #3 $49.91   11.610%   $55.7046   $55.70   $55.70   $55.70  
  Purchase #4 $70.54   11.241%   $78.4694   $78.47   $78.45   $78.50  
  Purchase #5 $68.30   7.447%   $73.3863   $73.39   $73.40   $73.40  
  Purchase #6 $204.81   12.833%   $231.0933   $231.09   $231.10   $231.10  
  Purchase #7 $156.41   9.618%   $171.4535   $171.45   $171.45   $171.50  
  7 purchase totals = $769.32       $853.3244   $853.31   $853.30   $853.40