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 $38.38   12.389%   $43.1349   $43.13   $43.15   $43.10  
  Purchase #2 $231.61   9.103%   $252.6935   $252.69   $252.70   $252.70  
  Purchase #3 $242.37   13.135%   $274.2053   $274.21   $274.20   $274.20  
  Purchase #4 $45.82   11.112%   $50.9115   $50.91   $50.90   $50.90  
  Purchase #5 $247.37   8.137%   $267.4985   $267.50   $267.50   $267.50  
  Purchase #6 $140.93   3.245%   $145.5032   $145.50   $145.50   $145.50  
  Purchase #7 $115.67   13.516%   $131.304   $131.30   $131.30   $131.30  
  7 purchase totals = $1,062.15       $1,165.2509   $1,165.24   $1,165.25   $1,165.20