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 $244.99   3.761%   $254.2041   $254.20   $254.20   $254.20  
  Purchase #2 $64.90   4.485%   $67.8108   $67.81   $67.80   $67.80  
  Purchase #3 $78.39   3.476%   $81.1148   $81.11   $81.10   $81.10  
  Purchase #4 $138.53   4.445%   $144.6877   $144.69   $144.70   $144.70  
  Purchase #5 $122.78   12.340%   $137.9311   $137.93   $137.95   $137.90  
  Purchase #6 $140.75   3.315%   $145.4159   $145.42   $145.40   $145.40  
  Purchase #7 $233.68   6.302%   $248.4065   $248.41   $248.40   $248.40  
  7 purchase totals = $1,024.02       $1,079.5709   $1,079.57   $1,079.55   $1,079.50