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 $76.43   11.604%   $85.2989   $85.30   $85.30   $85.30  
  Purchase #2 $77.46   4.178%   $80.6963   $80.70   $80.70   $80.70  
  Purchase #3 $62.32   8.695%   $67.7387   $67.74   $67.75   $67.70  
  Purchase #4 $159.82   5.703%   $168.9345   $168.93   $168.95   $168.90  
  Purchase #5 $152.82   4.314%   $159.4127   $159.41   $159.40   $159.40  
  Purchase #6 $43.26   3.676%   $44.8502   $44.85   $44.85   $44.90  
  Purchase #7 $179.58   3.731%   $186.2801   $186.28   $186.30   $186.30  
  7 purchase totals = $751.69       $793.2114   $793.21   $793.25   $793.20