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 $75.46   13.727%   $85.8184   $85.82   $85.80   $85.80  
  Purchase #2 $155.73   3.224%   $160.7507   $160.75   $160.75   $160.80  
  Purchase #3 $140.35   8.354%   $152.0748   $152.07   $152.05   $152.10  
  Purchase #4 $51.87   7.235%   $55.6228   $55.62   $55.60   $55.60  
  Purchase #5 $219.47   4.716%   $229.8202   $229.82   $229.80   $229.80  
  Purchase #6 $113.61   11.117%   $126.24   $126.24   $126.25   $126.20  
  Purchase #7 $175.44   5.307%   $184.7506   $184.75   $184.75   $184.80  
  7 purchase totals = $931.93       $995.0775   $995.07   $995.00   $995.10