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 $243.61   13.597%   $276.7337   $276.73   $276.75   $276.70  
  Purchase #2 $78.62   6.470%   $83.7067   $83.71   $83.70   $83.70  
  Purchase #3 $101.38   7.817%   $109.3049   $109.30   $109.30   $109.30  
  Purchase #4 $166.37   7.538%   $178.911   $178.91   $178.90   $178.90  
  Purchase #5 $181.55   6.445%   $193.2509   $193.25   $193.25   $193.30  
  Purchase #6 $21.72   12.287%   $24.3887   $24.39   $24.40   $24.40  
  Purchase #7 $225.68   9.187%   $246.4132   $246.41   $246.40   $246.40  
  7 purchase totals = $1,018.93       $1,112.7091   $1,112.70   $1,112.70   $1,112.70