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 $34.91   5.561%   $36.8513   $36.85   $36.85   $36.90  
  Purchase #2 $164.50   7.388%   $176.6533   $176.65   $176.65   $176.70  
  Purchase #3 $142.60   13.443%   $161.7697   $161.77   $161.75   $161.80  
  Purchase #4 $212.76   8.436%   $230.7084   $230.71   $230.70   $230.70  
  Purchase #5 $49.63   3.304%   $51.2698   $51.27   $51.25   $51.30  
  Purchase #6 $165.79   6.502%   $176.5697   $176.57   $176.55   $176.60  
  Purchase #7 $36.28   8.853%   $39.4919   $39.49   $39.50   $39.50  
  7 purchase totals = $806.47       $873.3141   $873.31   $873.25   $873.50