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 $32.30   6.703%   $34.4651   $34.47   $34.45   $34.50  
  Purchase #2 $153.43   13.682%   $174.4223   $174.42   $174.40   $174.40  
  Purchase #3 $105.32   12.543%   $118.5303   $118.53   $118.55   $118.50  
  Purchase #4 $114.81   4.866%   $120.3967   $120.40   $120.40   $120.40  
  Purchase #5 $168.77   12.188%   $189.3397   $189.34   $189.35   $189.30  
  Purchase #6 $248.64   12.473%   $279.6529   $279.65   $279.65   $279.70  
  Purchase #7 $188.65   6.825%   $201.5254   $201.53   $201.55   $201.50  
  7 purchase totals = $1,011.92       $1,118.3324   $1,118.34   $1,118.35   $1,118.30