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 $61.56   7.139%   $65.9548   $65.95   $65.95   $66.00  
  Purchase #2 $204.75   6.267%   $217.5817   $217.58   $217.60   $217.60  
  Purchase #3 $111.67   5.103%   $117.3685   $117.37   $117.35   $117.40  
  Purchase #4 $138.40   4.511%   $144.6432   $144.64   $144.65   $144.60  
  Purchase #5 $67.60   8.714%   $73.4907   $73.49   $73.50   $73.50  
  Purchase #6 $196.73   5.350%   $207.2551   $207.26   $207.25   $207.30  
  Purchase #7 $9.69   13.717%   $11.0192   $11.02   $11.00   $11.00  
  7 purchase totals = $790.40       $837.3132   $837.31   $837.30   $837.40