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 $248.35   10.587%   $274.6428   $274.64   $274.65   $274.60  
  Purchase #2 $236.85   12.107%   $265.5254   $265.53   $265.55   $265.50  
  Purchase #3 $119.66   9.806%   $131.3939   $131.39   $131.40   $131.40  
  Purchase #4 $178.70   10.505%   $197.4724   $197.47   $197.45   $197.50  
  Purchase #5 $27.82   9.630%   $30.4991   $30.50   $30.50   $30.50  
  Purchase #6 $151.47   3.198%   $156.314   $156.31   $156.30   $156.30  
  Purchase #7 $61.93   10.651%   $68.5262   $68.53   $68.55   $68.50  
  7 purchase totals = $1,024.78       $1,124.3738   $1,124.37   $1,124.40   $1,124.30