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 $184.66   9.215%   $201.6764   $201.68   $201.70   $201.70  
  Purchase #2 $87.71   5.132%   $92.2113   $92.21   $92.20   $92.20  
  Purchase #3 $227.27   7.274%   $243.8016   $243.80   $243.80   $243.80  
  Purchase #4 $43.40   3.855%   $45.0731   $45.07   $45.05   $45.10  
  Purchase #5 $112.91   6.448%   $120.1904   $120.19   $120.20   $120.20  
  Purchase #6 $208.77   11.723%   $233.2441   $233.24   $233.25   $233.20  
  Purchase #7 $92.97   11.809%   $103.9488   $103.95   $103.95   $103.90  
  7 purchase totals = $957.69       $1,040.1457   $1,040.14   $1,040.15   $1,040.10