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 $23.99   6.497%   $25.5486   $25.55   $25.55   $25.50  
  Purchase #2 $150.55   11.574%   $167.9747   $167.97   $167.95   $168.00  
  Purchase #3 $247.75   11.413%   $276.0257   $276.03   $276.05   $276.00  
  Purchase #4 $237.35   4.174%   $247.257   $247.26   $247.25   $247.30  
  Purchase #5 $226.73   10.503%   $250.5435   $250.54   $250.55   $250.50  
  Purchase #6 $111.89   6.636%   $119.315   $119.32   $119.30   $119.30  
  Purchase #7 $182.80   6.785%   $195.203   $195.20   $195.20   $195.20  
  7 purchase totals = $1,181.06       $1,281.8675   $1,281.87   $1,281.85   $1,281.80