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 $183.75   12.205%   $206.1767   $206.18   $206.20   $206.20  
  Purchase #2 $166.39   4.725%   $174.2519   $174.25   $174.25   $174.30  
  Purchase #3 $83.27   11.500%   $92.8461   $92.85   $92.85   $92.80  
  Purchase #4 $91.53   4.127%   $95.3074   $95.31   $95.30   $95.30  
  Purchase #5 $170.65   5.680%   $180.3429   $180.34   $180.35   $180.30  
  Purchase #6 $116.75   11.750%   $130.4681   $130.47   $130.45   $130.50  
  Purchase #7 $200.81   10.547%   $221.9894   $221.99   $222.00   $222.00  
  7 purchase totals = $1,013.15       $1,101.3825   $1,101.39   $1,101.40   $1,101.40