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 $245.85   5.253%   $258.7645   $258.76   $258.75   $258.80  
  Purchase #2 $206.55   4.609%   $216.0699   $216.07   $216.05   $216.10  
  Purchase #3 $134.52   12.397%   $151.1964   $151.20   $151.20   $151.20  
  Purchase #4 $95.80   4.645%   $100.2499   $100.25   $100.25   $100.20  
  Purchase #5 $166.80   10.813%   $184.8361   $184.84   $184.85   $184.80  
  Purchase #6 $123.66   8.165%   $133.7568   $133.76   $133.75   $133.80  
  Purchase #7 $158.78   8.746%   $172.6669   $172.67   $172.65   $172.70  
  7 purchase totals = $1,131.96       $1,217.5405   $1,217.55   $1,217.50   $1,217.60