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 $69.86   6.328%   $74.2807   $74.28   $74.30   $74.30  
  Purchase #2 $244.43   5.333%   $257.4655   $257.47   $257.45   $257.50  
  Purchase #3 $16.50   5.788%   $17.455   $17.46   $17.45   $17.50  
  Purchase #4 $226.87   12.604%   $255.4647   $255.46   $255.45   $255.50  
  Purchase #5 $69.75   8.469%   $75.6571   $75.66   $75.65   $75.70  
  Purchase #6 $189.44   12.358%   $212.851   $212.85   $212.85   $212.90  
  Purchase #7 $223.64   11.252%   $248.804   $248.80   $248.80   $248.80  
  7 purchase totals = $1,040.49       $1,141.9780   $1,141.98   $1,141.95   $1,142.20