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 $183.35   12.175%   $205.6729   $205.67   $205.65   $205.70  
  Purchase #2 $43.25   7.789%   $46.6187   $46.62   $46.60   $46.60  
  Purchase #3 $90.89   5.586%   $95.9671   $95.97   $95.95   $96.00  
  Purchase #4 $72.80   12.307%   $81.7595   $81.76   $81.75   $81.80  
  Purchase #5 $111.74   9.117%   $121.9273   $121.93   $121.95   $121.90  
  Purchase #6 $210.42   10.259%   $232.007   $232.01   $232.00   $232.00  
  Purchase #7 $69.53   8.822%   $75.6639   $75.66   $75.65   $75.70  
  7 purchase totals = $781.98       $859.6164   $859.62   $859.55   $859.70