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 $88.79   8.306%   $96.1649   $96.16   $96.15   $96.20  
  Purchase #2 $17.78   10.634%   $19.6707   $19.67   $19.65   $19.70  
  Purchase #3 $191.38   3.256%   $197.6113   $197.61   $197.60   $197.60  
  Purchase #4 $197.27   12.136%   $221.2107   $221.21   $221.20   $221.20  
  Purchase #5 $226.64   8.703%   $246.3645   $246.36   $246.35   $246.40  
  Purchase #6 $214.41   9.307%   $234.3651   $234.37   $234.35   $234.40  
  Purchase #7 $8.32   12.753%   $9.381   $9.38   $9.40   $9.40  
  7 purchase totals = $944.59       $1,024.7682   $1,024.76   $1,024.70   $1,024.90