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 $46.94   11.708%   $52.4357   $52.44   $52.45   $52.40  
  Purchase #2 $61.55   5.721%   $65.0713   $65.07   $65.05   $65.10  
  Purchase #3 $84.61   3.271%   $87.3776   $87.38   $87.40   $87.40  
  Purchase #4 $218.37   7.128%   $233.9354   $233.94   $233.95   $233.90  
  Purchase #5 $201.82   11.111%   $224.2442   $224.24   $224.25   $224.20  
  Purchase #6 $173.78   10.666%   $192.3154   $192.32   $192.30   $192.30  
  Purchase #7 $97.89   8.610%   $106.3183   $106.32   $106.30   $106.30  
  7 purchase totals = $884.96       $961.6979   $961.71   $961.70   $961.60