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 $242.55   10.607%   $268.2773   $268.28   $268.30   $268.30  
  Purchase #2 $239.59   12.265%   $268.9757   $268.98   $269.00   $269.00  
  Purchase #3 $39.66   9.696%   $43.5054   $43.51   $43.50   $43.50  
  Purchase #4 $57.77   6.434%   $61.4869   $61.49   $61.50   $61.50  
  Purchase #5 $219.40   3.270%   $226.5744   $226.57   $226.55   $226.60  
  Purchase #6 $5.48   6.697%   $5.847   $5.85   $5.85   $5.80  
  Purchase #7 $207.97   5.353%   $219.1026   $219.10   $219.10   $219.10  
  7 purchase totals = $1,012.42       $1,093.7693   $1,093.78   $1,093.80   $1,093.80