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 $184.82   7.344%   $198.3932   $198.39   $198.40   $198.40  
  Purchase #2 $214.36   13.417%   $243.1207   $243.12   $243.10   $243.10  
  Purchase #3 $225.50   7.718%   $242.9041   $242.90   $242.90   $242.90  
  Purchase #4 $216.45   10.468%   $239.108   $239.11   $239.10   $239.10  
  Purchase #5 $72.55   11.786%   $81.1007   $81.10   $81.10   $81.10  
  Purchase #6 $155.85   9.116%   $170.0573   $170.06   $170.05   $170.10  
  Purchase #7 $190.37   8.381%   $206.3249   $206.32   $206.30   $206.30  
  7 purchase totals = $1,259.90       $1,381.0089   $1,381.00   $1,380.95   $1,381.00