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 $161.96   3.808%   $168.1274   $168.13   $168.15   $168.10  
  Purchase #2 $70.94   8.407%   $76.9039   $76.90   $76.90   $76.90  
  Purchase #3 $94.68   6.188%   $100.5388   $100.54   $100.55   $100.50  
  Purchase #4 $44.76   8.811%   $48.7038   $48.70   $48.70   $48.70  
  Purchase #5 $237.39   13.731%   $269.986   $269.99   $270.00   $270.00  
  Purchase #6 $174.94   10.660%   $193.5886   $193.59   $193.60   $193.60  
  Purchase #7 $161.39   3.816%   $167.5486   $167.55   $167.55   $167.50  
  7 purchase totals = $946.06       $1,025.3971   $1,025.40   $1,025.45   $1,025.30