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 $62.38   4.271%   $65.0442   $65.04   $65.05   $65.00  
  Purchase #2 $89.64   9.691%   $98.327   $98.33   $98.35   $98.30  
  Purchase #3 $137.61   11.138%   $152.937   $152.94   $152.95   $152.90  
  Purchase #4 $131.86   13.444%   $149.5873   $149.59   $149.60   $149.60  
  Purchase #5 $96.86   9.488%   $106.0501   $106.05   $106.05   $106.10  
  Purchase #6 $198.67   9.731%   $218.0026   $218.00   $218.00   $218.00  
  Purchase #7 $40.42   7.551%   $43.4721   $43.47   $43.45   $43.50  
  7 purchase totals = $757.44       $833.4203   $833.42   $833.45   $833.40