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 $93.97   10.491%   $103.8284   $103.83   $103.85   $103.80  
  Purchase #2 $207.34   8.848%   $225.6854   $225.69   $225.70   $225.70  
  Purchase #3 $216.26   8.439%   $234.5102   $234.51   $234.50   $234.50  
  Purchase #4 $20.57   11.663%   $22.9691   $22.97   $22.95   $23.00  
  Purchase #5 $146.35   7.439%   $157.237   $157.24   $157.25   $157.20  
  Purchase #6 $113.98   4.385%   $118.978   $118.98   $119.00   $119.00  
  Purchase #7 $153.36   10.323%   $169.1914   $169.19   $169.20   $169.20  
  7 purchase totals = $951.83       $1,032.3995   $1,032.41   $1,032.45   $1,032.40