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 $152.86   9.810%   $167.8556   $167.86   $167.85   $167.90  
  Purchase #2 $117.30   11.172%   $130.4048   $130.40   $130.40   $130.40  
  Purchase #3 $10.81   8.358%   $11.7135   $11.71   $11.70   $11.70  
  Purchase #4 $205.55   13.521%   $233.3424   $233.34   $233.35   $233.30  
  Purchase #5 $150.90   13.448%   $171.193   $171.19   $171.20   $171.20  
  Purchase #6 $67.66   8.628%   $73.4977   $73.50   $73.50   $73.50  
  Purchase #7 $111.40   12.794%   $125.6525   $125.65   $125.65   $125.70  
  7 purchase totals = $816.48       $913.6595   $913.65   $913.65   $913.70