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 $246.67   5.773%   $260.9103   $260.91   $260.90   $260.90  
  Purchase #2 $140.49   11.533%   $156.6927   $156.69   $156.70   $156.70  
  Purchase #3 $81.85   6.773%   $87.3937   $87.39   $87.40   $87.40  
  Purchase #4 $200.86   11.109%   $223.1735   $223.17   $223.15   $223.20  
  Purchase #5 $201.67   8.723%   $219.2617   $219.26   $219.25   $219.30  
  Purchase #6 $136.75   10.714%   $151.4014   $151.40   $151.40   $151.40  
  Purchase #7 $172.74   11.790%   $193.106   $193.11   $193.10   $193.10  
  7 purchase totals = $1,181.03       $1,291.9393   $1,291.93   $1,291.90   $1,292.00