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 $90.67   11.710%   $101.2875   $101.29   $101.30   $101.30  
  Purchase #2 $218.39   13.869%   $248.6785   $248.68   $248.70   $248.70  
  Purchase #3 $211.25   6.138%   $224.2165   $224.22   $224.20   $224.20  
  Purchase #4 $245.33   6.195%   $260.5282   $260.53   $260.55   $260.50  
  Purchase #5 $162.81   13.544%   $184.861   $184.86   $184.85   $184.90  
  Purchase #6 $147.36   5.576%   $155.5768   $155.58   $155.60   $155.60  
  Purchase #7 $81.36   8.513%   $88.2862   $88.29   $88.30   $88.30  
  7 purchase totals = $1,157.17       $1,263.4347   $1,263.45   $1,263.50   $1,263.50