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 $131.31   13.671%   $149.2614   $149.26   $149.25   $149.30  
  Purchase #2 $113.38   6.423%   $120.6624   $120.66   $120.65   $120.70  
  Purchase #3 $120.38   10.492%   $133.0103   $133.01   $133.00   $133.00  
  Purchase #4 $50.74   6.834%   $54.2076   $54.21   $54.20   $54.20  
  Purchase #5 $88.76   6.138%   $94.2081   $94.21   $94.20   $94.20  
  Purchase #6 $241.59   3.131%   $249.1542   $249.15   $249.15   $249.20  
  Purchase #7 $234.94   4.156%   $244.7041   $244.70   $244.70   $244.70  
  7 purchase totals = $981.10       $1,045.2081   $1,045.20   $1,045.15   $1,045.30