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 $92.83   3.433%   $96.0169   $96.02   $96.00   $96.00  
  Purchase #2 $101.64   4.522%   $106.2362   $106.24   $106.25   $106.20  
  Purchase #3 $174.61   13.723%   $198.5717   $198.57   $198.55   $198.60  
  Purchase #4 $249.95   7.722%   $269.2511   $269.25   $269.25   $269.30  
  Purchase #5 $89.43   7.529%   $96.1632   $96.16   $96.15   $96.20  
  Purchase #6 $176.33   13.717%   $200.5172   $200.52   $200.50   $200.50  
  Purchase #7 $76.67   8.436%   $83.1379   $83.14   $83.15   $83.10  
  7 purchase totals = $961.46       $1,049.8942   $1,049.90   $1,049.85   $1,049.90