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 $223.33   13.841%   $254.2411   $254.24   $254.25   $254.20  
  Purchase #2 $219.36   9.705%   $240.6489   $240.65   $240.65   $240.60  
  Purchase #3 $243.87   8.834%   $265.4135   $265.41   $265.40   $265.40  
  Purchase #4 $177.55   5.257%   $186.8838   $186.88   $186.90   $186.90  
  Purchase #5 $8.49   4.246%   $8.8505   $8.85   $8.85   $8.90  
  Purchase #6 $172.57   11.380%   $192.2085   $192.21   $192.20   $192.20  
  Purchase #7 $233.56   13.718%   $265.5998   $265.60   $265.60   $265.60  
  7 purchase totals = $1,278.73       $1,413.8461   $1,413.84   $1,413.85   $1,413.80