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 $87.85   12.509%   $98.8392   $98.84   $98.85   $98.80  
  Purchase #2 $107.77   10.416%   $118.9953   $119.00   $119.00   $119.00  
  Purchase #3 $184.95   5.687%   $195.4681   $195.47   $195.45   $195.50  
  Purchase #4 $167.97   7.344%   $180.3057   $180.31   $180.30   $180.30  
  Purchase #5 $133.61   13.793%   $152.0388   $152.04   $152.05   $152.00  
  Purchase #6 $111.68   7.112%   $119.6227   $119.62   $119.60   $119.60  
  Purchase #7 $146.85   4.143%   $152.934   $152.93   $152.95   $152.90  
  7 purchase totals = $940.68       $1,018.2038   $1,018.21   $1,018.20   $1,018.10