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 $185.95   13.787%   $211.5869   $211.59   $211.60   $211.60  
  Purchase #2 $61.44   11.284%   $68.3729   $68.37   $68.35   $68.40  
  Purchase #3 $36.87   9.565%   $40.3966   $40.40   $40.40   $40.40  
  Purchase #4 $64.94   7.190%   $69.6092   $69.61   $69.60   $69.60  
  Purchase #5 $181.54   12.533%   $204.2924   $204.29   $204.30   $204.30  
  Purchase #6 $149.81   8.408%   $162.406   $162.41   $162.40   $162.40  
  Purchase #7 $40.47   3.619%   $41.9346   $41.93   $41.95   $41.90  
  7 purchase totals = $721.02       $798.5986   $798.60   $798.60   $798.60