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 $206.75   10.619%   $228.7048   $228.70   $228.70   $228.70  
  Purchase #2 $115.55   8.263%   $125.0979   $125.10   $125.10   $125.10  
  Purchase #3 $55.99   12.453%   $62.9624   $62.96   $62.95   $63.00  
  Purchase #4 $129.69   4.141%   $135.0605   $135.06   $135.05   $135.10  
  Purchase #5 $178.91   3.105%   $184.4652   $184.47   $184.45   $184.50  
  Purchase #6 $197.57   10.390%   $218.0975   $218.10   $218.10   $218.10  
  Purchase #7 $156.76   10.675%   $173.4941   $173.49   $173.50   $173.50  
  7 purchase totals = $1,041.22       $1,127.8824   $1,127.88   $1,127.85   $1,128.00