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 $67.47   13.701%   $76.7141   $76.71   $76.70   $76.70  
  Purchase #2 $124.44   6.519%   $132.5522   $132.55   $132.55   $132.60  
  Purchase #3 $12.49   8.295%   $13.526   $13.53   $13.55   $13.50  
  Purchase #4 $56.99   4.784%   $59.7164   $59.72   $59.70   $59.70  
  Purchase #5 $101.37   4.668%   $106.102   $106.10   $106.10   $106.10  
  Purchase #6 $235.93   12.204%   $264.7229   $264.72   $264.70   $264.70  
  Purchase #7 $183.71   4.744%   $192.4252   $192.43   $192.45   $192.40  
  7 purchase totals = $782.40       $845.7588   $845.76   $845.75   $845.70