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 $66.76   10.172%   $73.5508   $73.55   $73.55   $73.60  
  Purchase #2 $81.94   13.216%   $92.7692   $92.77   $92.75   $92.80  
  Purchase #3 $15.69   12.635%   $17.6724   $17.67   $17.65   $17.70  
  Purchase #4 $108.43   9.553%   $118.7883   $118.79   $118.80   $118.80  
  Purchase #5 $86.62   11.582%   $96.6523   $96.65   $96.65   $96.70  
  Purchase #6 $168.69   4.603%   $176.4548   $176.45   $176.45   $176.50  
  Purchase #7 $149.66   10.287%   $165.0555   $165.06   $165.05   $165.10  
  7 purchase totals = $677.79       $740.9433   $740.94   $740.90   $741.20