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 $184.36   4.653%   $192.9383   $192.94   $192.95   $192.90  
  Purchase #2 $43.73   13.871%   $49.7958   $49.80   $49.80   $49.80  
  Purchase #3 $84.66   5.810%   $89.5787   $89.58   $89.60   $89.60  
  Purchase #4 $6.89   8.125%   $7.4498   $7.45   $7.45   $7.40  
  Purchase #5 $237.40   10.460%   $262.232   $262.23   $262.25   $262.20  
  Purchase #6 $195.36   9.806%   $214.517   $214.52   $214.50   $214.50  
  Purchase #7 $201.26   11.814%   $225.0369   $225.04   $225.05   $225.00  
  7 purchase totals = $953.66       $1,041.5485   $1,041.56   $1,041.60   $1,041.40