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 $8.36   7.636%   $8.9984   $9.00   $9.00   $9.00  
  Purchase #2 $247.29   9.286%   $270.2533   $270.25   $270.25   $270.30  
  Purchase #3 $105.96   8.646%   $115.1213   $115.12   $115.10   $115.10  
  Purchase #4 $143.30   5.287%   $150.8763   $150.88   $150.90   $150.90  
  Purchase #5 $100.97   10.607%   $111.6799   $111.68   $111.70   $111.70  
  Purchase #6 $25.31   6.549%   $26.9676   $26.97   $26.95   $27.00  
  Purchase #7 $29.61   9.510%   $32.4259   $32.43   $32.45   $32.40  
  7 purchase totals = $660.80       $716.3227   $716.33   $716.35   $716.40