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 $38.38   13.808%   $43.6795   $43.68   $43.70   $43.70  
  Purchase #2 $152.65   10.152%   $168.147   $168.15   $168.15   $168.10  
  Purchase #3 $58.54   4.540%   $61.1977   $61.20   $61.20   $61.20  
  Purchase #4 $49.41   6.358%   $52.5515   $52.55   $52.55   $52.60  
  Purchase #5 $125.43   7.130%   $134.3732   $134.37   $134.35   $134.40  
  Purchase #6 $162.98   8.524%   $176.8724   $176.87   $176.85   $176.90  
  Purchase #7 $167.54   12.278%   $188.1106   $188.11   $188.10   $188.10  
  7 purchase totals = $754.93       $824.9319   $824.93   $824.90   $825.00