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 $206.77   13.471%   $234.624   $234.62   $234.60   $234.60  
  Purchase #2 $127.49   10.576%   $140.9733   $140.97   $140.95   $141.00  
  Purchase #3 $10.80   6.337%   $11.4844   $11.48   $11.50   $11.50  
  Purchase #4 $189.78   13.138%   $214.7133   $214.71   $214.70   $214.70  
  Purchase #5 $212.95   9.188%   $232.5158   $232.52   $232.50   $232.50  
  Purchase #6 $67.75   8.197%   $73.3035   $73.30   $73.30   $73.30  
  Purchase #7 $234.72   6.113%   $249.0684   $249.07   $249.05   $249.10  
  7 purchase totals = $1,050.26       $1,156.6827   $1,156.67   $1,156.60   $1,156.70