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 $155.83   13.376%   $176.6738   $176.67   $176.65   $176.70  
  Purchase #2 $217.41   9.767%   $238.6444   $238.64   $238.65   $238.60  
  Purchase #3 $62.75   5.707%   $66.3311   $66.33   $66.35   $66.30  
  Purchase #4 $161.31   12.674%   $181.7544   $181.75   $181.75   $181.80  
  Purchase #5 $86.62   9.504%   $94.8524   $94.85   $94.85   $94.90  
  Purchase #6 $218.67   9.560%   $239.5749   $239.57   $239.55   $239.60  
  Purchase #7 $237.63   12.656%   $267.7045   $267.70   $267.70   $267.70  
  7 purchase totals = $1,140.22       $1,265.5355   $1,265.51   $1,265.50   $1,265.60