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 $92.41   12.759%   $104.2006   $104.20   $104.20   $104.20  
  Purchase #2 $128.80   11.796%   $143.9932   $143.99   $144.00   $144.00  
  Purchase #3 $180.25   9.586%   $197.5288   $197.53   $197.55   $197.50  
  Purchase #4 $166.69   13.687%   $189.5049   $189.50   $189.50   $189.50  
  Purchase #5 $13.39   9.731%   $14.693   $14.69   $14.70   $14.70  
  Purchase #6 $250.42   4.723%   $262.2473   $262.25   $262.25   $262.20  
  Purchase #7 $241.57   3.657%   $250.4042   $250.40   $250.40   $250.40  
  7 purchase totals = $1,073.53       $1,162.5720   $1,162.56   $1,162.60   $1,162.50