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 $111.58   6.233%   $118.5348   $118.53   $118.55   $118.50  
  Purchase #2 $124.74   9.362%   $136.4182   $136.42   $136.40   $136.40  
  Purchase #3 $111.45   7.629%   $119.9525   $119.95   $119.95   $120.00  
  Purchase #4 $61.49   13.518%   $69.8022   $69.80   $69.80   $69.80  
  Purchase #5 $32.45   13.656%   $36.8814   $36.88   $36.90   $36.90  
  Purchase #6 $213.58   10.366%   $235.7197   $235.72   $235.70   $235.70  
  Purchase #7 $182.42   7.611%   $196.304   $196.30   $196.30   $196.30  
  7 purchase totals = $837.71       $913.6128   $913.60   $913.60   $913.60