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 $8.66   10.174%   $9.5411   $9.54   $9.55   $9.50  
  Purchase #2 $121.84   8.358%   $132.0234   $132.02   $132.00   $132.00  
  Purchase #3 $132.44   8.243%   $143.357   $143.36   $143.35   $143.40  
  Purchase #4 $178.32   6.169%   $189.3206   $189.32   $189.30   $189.30  
  Purchase #5 $5.64   5.487%   $5.9495   $5.95   $5.95   $5.90  
  Purchase #6 $133.70   11.762%   $149.4258   $149.43   $149.45   $149.40  
  Purchase #7 $208.87   6.481%   $222.4069   $222.41   $222.40   $222.40  
  7 purchase totals = $789.47       $852.0243   $852.03   $852.00   $851.90