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 $51.48   5.716%   $54.4226   $54.42   $54.40   $54.40  
  Purchase #2 $208.56   11.185%   $231.8874   $231.89   $231.90   $231.90  
  Purchase #3 $27.45   6.365%   $29.1972   $29.20   $29.20   $29.20  
  Purchase #4 $55.31   8.340%   $59.9229   $59.92   $59.90   $59.90  
  Purchase #5 $134.25   4.435%   $140.204   $140.20   $140.20   $140.20  
  Purchase #6 $181.69   13.488%   $206.1963   $206.20   $206.20   $206.20  
  Purchase #7 $32.71   6.222%   $34.7452   $34.75   $34.75   $34.70  
  7 purchase totals = $691.45       $756.5756   $756.58   $756.55   $756.50