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 $71.65   4.324%   $74.7481   $74.75   $74.75   $74.70  
  Purchase #2 $131.68   6.574%   $140.3366   $140.34   $140.35   $140.30  
  Purchase #3 $177.90   13.605%   $202.1033   $202.10   $202.10   $202.10  
  Purchase #4 $146.42   4.124%   $152.4584   $152.46   $152.45   $152.50  
  Purchase #5 $196.47   3.782%   $203.9005   $203.90   $203.90   $203.90  
  Purchase #6 $22.91   9.493%   $25.0848   $25.08   $25.10   $25.10  
  Purchase #7 $212.34   6.327%   $225.7748   $225.77   $225.75   $225.80  
  7 purchase totals = $959.37       $1,024.4065   $1,024.40   $1,024.40   $1,024.40