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 $78.91   6.364%   $83.9318   $83.93   $83.95   $83.90  
  Purchase #2 $204.60   13.682%   $232.5934   $232.59   $232.60   $232.60  
  Purchase #3 $249.83   13.353%   $283.1898   $283.19   $283.20   $283.20  
  Purchase #4 $206.64   3.691%   $214.2671   $214.27   $214.25   $214.30  
  Purchase #5 $32.97   13.133%   $37.3   $37.30   $37.30   $37.30  
  Purchase #6 $160.43   10.298%   $176.9511   $176.95   $176.95   $177.00  
  Purchase #7 $47.41   4.824%   $49.6971   $49.70   $49.70   $49.70  
  7 purchase totals = $980.79       $1,077.9303   $1,077.93   $1,077.95   $1,078.00