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 $248.39   10.308%   $273.994   $273.99   $274.00   $274.00  
  Purchase #2 $160.44   10.854%   $177.8542   $177.85   $177.85   $177.90  
  Purchase #3 $32.47   8.582%   $35.2566   $35.26   $35.25   $35.30  
  Purchase #4 $211.70   6.757%   $226.0046   $226.00   $226.00   $226.00  
  Purchase #5 $5.27   6.408%   $5.6077   $5.61   $5.60   $5.60  
  Purchase #6 $181.84   13.517%   $206.4193   $206.42   $206.40   $206.40  
  Purchase #7 $17.83   10.209%   $19.6503   $19.65   $19.65   $19.70  
  7 purchase totals = $857.94       $944.7867   $944.78   $944.75   $944.90