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 $148.95   10.742%   $164.9502   $164.95   $164.95   $165.00  
  Purchase #2 $176.49   9.307%   $192.9159   $192.92   $192.90   $192.90  
  Purchase #3 $30.84   5.603%   $32.568   $32.57   $32.55   $32.60  
  Purchase #4 $226.76   13.433%   $257.2207   $257.22   $257.20   $257.20  
  Purchase #5 $61.84   4.518%   $64.6339   $64.63   $64.65   $64.60  
  Purchase #6 $211.73   13.380%   $240.0595   $240.06   $240.05   $240.10  
  Purchase #7 $233.90   9.479%   $256.0714   $256.07   $256.05   $256.10  
  7 purchase totals = $1,090.51       $1,208.4196   $1,208.42   $1,208.35   $1,208.50