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 $81.87   8.283%   $88.6513   $88.65   $88.65   $88.70  
  Purchase #2 $150.78   13.544%   $171.2016   $171.20   $171.20   $171.20  
  Purchase #3 $70.42   8.614%   $76.486   $76.49   $76.50   $76.50  
  Purchase #4 $56.57   4.202%   $58.9471   $58.95   $58.95   $58.90  
  Purchase #5 $216.66   5.238%   $228.0087   $228.01   $228.00   $228.00  
  Purchase #6 $205.63   12.405%   $231.1384   $231.14   $231.15   $231.10  
  Purchase #7 $161.81   8.330%   $175.2888   $175.29   $175.30   $175.30  
  7 purchase totals = $943.74       $1,029.7219   $1,029.73   $1,029.75   $1,029.70