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 $24.46   8.374%   $26.5083   $26.51   $26.50   $26.50  
  Purchase #2 $171.25   13.413%   $194.2198   $194.22   $194.20   $194.20  
  Purchase #3 $45.63   11.640%   $50.9413   $50.94   $50.95   $50.90  
  Purchase #4 $246.46   12.860%   $278.1548   $278.15   $278.15   $278.20  
  Purchase #5 $127.65   10.839%   $141.486   $141.49   $141.50   $141.50  
  Purchase #6 $118.75   3.336%   $122.7115   $122.71   $122.70   $122.70  
  Purchase #7 $154.34   13.201%   $174.7144   $174.71   $174.70   $174.70  
  7 purchase totals = $888.54       $988.7361   $988.73   $988.70   $988.70