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 $186.47   6.744%   $199.0455   $199.05   $199.05   $199.00  
  Purchase #2 $187.58   8.676%   $203.8544   $203.85   $203.85   $203.90  
  Purchase #3 $21.97   3.312%   $22.6976   $22.70   $22.70   $22.70  
  Purchase #4 $183.71   11.446%   $204.7374   $204.74   $204.75   $204.70  
  Purchase #5 $131.75   4.195%   $137.2769   $137.28   $137.30   $137.30  
  Purchase #6 $186.37   5.394%   $196.4228   $196.42   $196.40   $196.40  
  Purchase #7 $61.65   6.106%   $65.4143   $65.41   $65.40   $65.40  
  7 purchase totals = $959.50       $1,029.4489   $1,029.45   $1,029.45   $1,029.40