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 $130.25   11.833%   $145.6625   $145.66   $145.65   $145.70  
  Purchase #2 $217.25   7.248%   $232.9963   $233.00   $233.00   $233.00  
  Purchase #3 $64.84   7.149%   $69.4754   $69.48   $69.50   $69.50  
  Purchase #4 $83.82   7.800%   $90.358   $90.36   $90.35   $90.40  
  Purchase #5 $192.65   5.491%   $203.2284   $203.23   $203.25   $203.20  
  Purchase #6 $95.26   10.454%   $105.2185   $105.22   $105.20   $105.20  
  Purchase #7 $75.55   10.136%   $83.2077   $83.21   $83.20   $83.20  
  7 purchase totals = $859.62       $930.1468   $930.16   $930.15   $930.20