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 $208.88   13.694%   $237.484   $237.48   $237.50   $237.50  
  Purchase #2 $74.65   11.176%   $82.9929   $82.99   $83.00   $83.00  
  Purchase #3 $212.33   13.271%   $240.5083   $240.51   $240.50   $240.50  
  Purchase #4 $233.65   13.710%   $265.6834   $265.68   $265.70   $265.70  
  Purchase #5 $151.53   6.656%   $161.6158   $161.62   $161.60   $161.60  
  Purchase #6 $243.34   9.717%   $266.9853   $266.99   $267.00   $267.00  
  Purchase #7 $139.87   4.323%   $145.9166   $145.92   $145.90   $145.90  
  7 purchase totals = $1,264.25       $1,401.1863   $1,401.19   $1,401.20   $1,401.20