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 $172.95   13.124%   $195.648   $195.65   $195.65   $195.60  
  Purchase #2 $164.42   3.703%   $170.5085   $170.51   $170.50   $170.50  
  Purchase #3 $92.34   9.363%   $100.9858   $100.99   $101.00   $101.00  
  Purchase #4 $175.56   4.471%   $183.4093   $183.41   $183.40   $183.40  
  Purchase #5 $17.70   13.420%   $20.0753   $20.08   $20.10   $20.10  
  Purchase #6 $134.77   12.748%   $151.9505   $151.95   $151.95   $152.00  
  Purchase #7 $161.80   4.847%   $169.6424   $169.64   $169.65   $169.60  
  7 purchase totals = $919.54       $992.2198   $992.23   $992.25   $992.20