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 $70.61   8.716%   $76.7644   $76.76   $76.75   $76.80  
  Purchase #2 $113.55   6.343%   $120.7525   $120.75   $120.75   $120.80  
  Purchase #3 $176.41   3.652%   $182.8525   $182.85   $182.85   $182.90  
  Purchase #4 $222.55   9.712%   $244.1641   $244.16   $244.15   $244.20  
  Purchase #5 $48.71   8.841%   $53.0165   $53.02   $53.00   $53.00  
  Purchase #6 $218.85   7.737%   $235.7824   $235.78   $235.80   $235.80  
  Purchase #7 $214.50   13.832%   $244.1696   $244.17   $244.15   $244.20  
  7 purchase totals = $1,065.18       $1,157.5020   $1,157.49   $1,157.45   $1,157.70