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 $61.71   9.802%   $67.7588   $67.76   $67.75   $67.80  
  Purchase #2 $132.86   6.158%   $141.0415   $141.04   $141.05   $141.00  
  Purchase #3 $133.39   11.469%   $148.6885   $148.69   $148.70   $148.70  
  Purchase #4 $237.39   11.403%   $264.4596   $264.46   $264.45   $264.50  
  Purchase #5 $150.93   6.730%   $161.0876   $161.09   $161.10   $161.10  
  Purchase #6 $144.92   10.836%   $160.6235   $160.62   $160.60   $160.60  
  Purchase #7 $7.71   10.754%   $8.5391   $8.54   $8.55   $8.50  
  7 purchase totals = $868.91       $952.1986   $952.20   $952.20   $952.20