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 $114.97   6.289%   $122.2005   $122.20   $122.20   $122.20  
  Purchase #2 $231.70   10.505%   $256.0401   $256.04   $256.05   $256.00  
  Purchase #3 $66.70   7.537%   $71.7272   $71.73   $71.75   $71.70  
  Purchase #4 $131.73   3.273%   $136.0415   $136.04   $136.05   $136.00  
  Purchase #5 $132.86   9.463%   $145.4325   $145.43   $145.45   $145.40  
  Purchase #6 $169.36   12.342%   $190.2624   $190.26   $190.25   $190.30  
  Purchase #7 $30.34   8.834%   $33.0202   $33.02   $33.00   $33.00  
  7 purchase totals = $877.66       $954.7244   $954.72   $954.75   $954.60