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 $84.72   13.430%   $96.0979   $96.10   $96.10   $96.10  
  Purchase #2 $70.62   8.156%   $76.3798   $76.38   $76.40   $76.40  
  Purchase #3 $24.89   8.782%   $27.0758   $27.08   $27.10   $27.10  
  Purchase #4 $159.94   10.335%   $176.4698   $176.47   $176.45   $176.50  
  Purchase #5 $156.60   5.543%   $165.2803   $165.28   $165.30   $165.30  
  Purchase #6 $106.38   11.471%   $118.5828   $118.58   $118.60   $118.60  
  Purchase #7 $164.89   6.408%   $175.4562   $175.46   $175.45   $175.50  
  7 purchase totals = $768.04       $835.3426   $835.35   $835.40   $835.50