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 $245.41   10.707%   $271.686   $271.69   $271.70   $271.70  
  Purchase #2 $110.25   8.437%   $119.5518   $119.55   $119.55   $119.60  
  Purchase #3 $5.53   13.815%   $6.294   $6.29   $6.30   $6.30  
  Purchase #4 $198.61   4.160%   $206.8722   $206.87   $206.85   $206.90  
  Purchase #5 $174.84   13.695%   $198.7843   $198.78   $198.80   $198.80  
  Purchase #6 $237.93   3.134%   $245.3867   $245.39   $245.40   $245.40  
  Purchase #7 $168.59   10.198%   $185.7828   $185.78   $185.80   $185.80  
  7 purchase totals = $1,141.16       $1,234.3578   $1,234.35   $1,234.40   $1,234.50