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 $114.62   9.326%   $125.3095   $125.31   $125.30   $125.30  
  Purchase #2 $203.44   5.642%   $214.9181   $214.92   $214.90   $214.90  
  Purchase #3 $55.25   10.320%   $60.9518   $60.95   $60.95   $61.00  
  Purchase #4 $82.99   4.376%   $86.6216   $86.62   $86.60   $86.60  
  Purchase #5 $41.70   4.753%   $43.682   $43.68   $43.70   $43.70  
  Purchase #6 $193.26   10.791%   $214.1147   $214.11   $214.10   $214.10  
  Purchase #7 $130.93   11.837%   $146.4282   $146.43   $146.45   $146.40  
  7 purchase totals = $822.19       $892.0259   $892.02   $892.00   $892.00