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 $58.83   10.406%   $64.9518   $64.95   $64.95   $65.00  
  Purchase #2 $132.87   8.372%   $143.9939   $143.99   $144.00   $144.00  
  Purchase #3 $206.86   5.395%   $218.0201   $218.02   $218.00   $218.00  
  Purchase #4 $155.38   12.441%   $174.7108   $174.71   $174.70   $174.70  
  Purchase #5 $140.96   8.143%   $152.4384   $152.44   $152.45   $152.40  
  Purchase #6 $174.30   5.414%   $183.7366   $183.74   $183.75   $183.70  
  Purchase #7 $33.66   7.359%   $36.137   $36.14   $36.15   $36.10  
  7 purchase totals = $902.86       $973.9886   $973.99   $974.00   $973.90