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 $173.63   6.774%   $185.3917   $185.39   $185.40   $185.40  
  Purchase #2 $216.31   5.190%   $227.5365   $227.54   $227.55   $227.50  
  Purchase #3 $184.80   9.133%   $201.6778   $201.68   $201.70   $201.70  
  Purchase #4 $59.66   13.231%   $67.5536   $67.55   $67.55   $67.60  
  Purchase #5 $208.60   9.150%   $227.6869   $227.69   $227.70   $227.70  
  Purchase #6 $167.56   8.765%   $182.2466   $182.25   $182.25   $182.20  
  Purchase #7 $108.66   3.603%   $112.575   $112.58   $112.60   $112.60  
  7 purchase totals = $1,119.22       $1,204.6681   $1,204.68   $1,204.75   $1,204.70