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 $202.26   4.812%   $211.9928   $211.99   $212.00   $212.00  
  Purchase #2 $101.77   8.319%   $110.2362   $110.24   $110.25   $110.20  
  Purchase #3 $151.30   11.104%   $168.1004   $168.10   $168.10   $168.10  
  Purchase #4 $241.34   11.736%   $269.6637   $269.66   $269.65   $269.70  
  Purchase #5 $58.32   13.278%   $66.0637   $66.06   $66.05   $66.10  
  Purchase #6 $195.57   5.669%   $206.6569   $206.66   $206.65   $206.70  
  Purchase #7 $200.34   3.574%   $207.5002   $207.50   $207.50   $207.50  
  7 purchase totals = $1,150.90       $1,240.2139   $1,240.21   $1,240.20   $1,240.30