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 $124.36   11.449%   $138.598   $138.60   $138.60   $138.60  
  Purchase #2 $178.36   4.342%   $186.1044   $186.10   $186.10   $186.10  
  Purchase #3 $59.33   10.873%   $65.781   $65.78   $65.80   $65.80  
  Purchase #4 $57.49   8.157%   $62.1795   $62.18   $62.20   $62.20  
  Purchase #5 $208.44   6.481%   $221.949   $221.95   $221.95   $221.90  
  Purchase #6 $97.46   11.775%   $108.9359   $108.94   $108.95   $108.90  
  Purchase #7 $239.92   10.335%   $264.7157   $264.72   $264.70   $264.70  
  7 purchase totals = $965.36       $1,048.2635   $1,048.27   $1,048.30   $1,048.20