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 $235.88   12.777%   $266.0184   $266.02   $266.00   $266.00  
  Purchase #2 $22.65   10.494%   $25.0269   $25.03   $25.05   $25.00  
  Purchase #3 $70.34   12.242%   $78.951   $78.95   $78.95   $79.00  
  Purchase #4 $6.93   13.176%   $7.8431   $7.84   $7.85   $7.80  
  Purchase #5 $214.80   5.619%   $226.8696   $226.87   $226.85   $226.90  
  Purchase #6 $175.34   11.586%   $195.6549   $195.65   $195.65   $195.70  
  Purchase #7 $183.81   7.435%   $197.4763   $197.48   $197.50   $197.50  
  7 purchase totals = $909.75       $997.8402   $997.84   $997.85   $997.90