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 $191.47   12.545%   $215.4899   $215.49   $215.50   $215.50  
  Purchase #2 $38.97   9.737%   $42.7645   $42.76   $42.75   $42.80  
  Purchase #3 $217.57   11.744%   $243.1214   $243.12   $243.10   $243.10  
  Purchase #4 $235.95   13.321%   $267.3809   $267.38   $267.40   $267.40  
  Purchase #5 $216.69   9.147%   $236.5106   $236.51   $236.50   $236.50  
  Purchase #6 $165.38   9.831%   $181.6385   $181.64   $181.65   $181.60  
  Purchase #7 $52.27   3.759%   $54.2348   $54.23   $54.25   $54.20  
  7 purchase totals = $1,118.30       $1,241.1406   $1,241.13   $1,241.15   $1,241.10