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 $176.62   7.767%   $190.3381   $190.34   $190.35   $190.30  
  Purchase #2 $60.32   8.571%   $65.49   $65.49   $65.50   $65.50  
  Purchase #3 $245.69   13.267%   $278.2857   $278.29   $278.30   $278.30  
  Purchase #4 $77.38   7.448%   $83.1433   $83.14   $83.15   $83.10  
  Purchase #5 $59.34   13.446%   $67.3189   $67.32   $67.30   $67.30  
  Purchase #6 $86.39   9.678%   $94.7508   $94.75   $94.75   $94.80  
  Purchase #7 $158.95   7.432%   $170.7632   $170.76   $170.75   $170.80  
  7 purchase totals = $864.69       $950.0900   $950.09   $950.10   $950.10