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 $66.87   9.209%   $73.0281   $73.03   $73.05   $73.00  
  Purchase #2 $219.68   5.463%   $231.6811   $231.68   $231.70   $231.70  
  Purchase #3 $12.53   5.321%   $13.1967   $13.20   $13.20   $13.20  
  Purchase #4 $118.63   4.226%   $123.6433   $123.64   $123.65   $123.60  
  Purchase #5 $233.65   5.463%   $246.4143   $246.41   $246.40   $246.40  
  Purchase #6 $64.84   7.646%   $69.7977   $69.80   $69.80   $69.80  
  Purchase #7 $177.89   13.536%   $201.9692   $201.97   $201.95   $202.00  
  7 purchase totals = $894.09       $959.7304   $959.73   $959.75   $959.70