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 $125.60   13.519%   $142.5799   $142.58   $142.60   $142.60  
  Purchase #2 $179.59   8.190%   $194.2984   $194.30   $194.30   $194.30  
  Purchase #3 $51.36   10.242%   $56.6203   $56.62   $56.60   $56.60  
  Purchase #4 $76.75   6.520%   $81.7541   $81.75   $81.75   $81.80  
  Purchase #5 $230.72   4.375%   $240.814   $240.81   $240.80   $240.80  
  Purchase #6 $230.30   9.479%   $252.1301   $252.13   $252.15   $252.10  
  Purchase #7 $49.78   11.647%   $55.5779   $55.58   $55.60   $55.60  
  7 purchase totals = $944.10       $1,023.7747   $1,023.77   $1,023.80   $1,023.80