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 $186.47   11.739%   $208.3597   $208.36   $208.35   $208.40  
  Purchase #2 $138.80   9.868%   $152.4968   $152.50   $152.50   $152.50  
  Purchase #3 $32.28   7.399%   $34.6684   $34.67   $34.65   $34.70  
  Purchase #4 $170.84   6.358%   $181.702   $181.70   $181.70   $181.70  
  Purchase #5 $147.69   9.189%   $161.2612   $161.26   $161.25   $161.30  
  Purchase #6 $195.74   7.653%   $210.72   $210.72   $210.70   $210.70  
  Purchase #7 $18.72   10.577%   $20.7   $20.70   $20.70   $20.70  
  7 purchase totals = $890.54       $969.9081   $969.91   $969.85   $970.00