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 $165.56   4.414%   $172.8678   $172.87   $172.85   $172.90  
  Purchase #2 $121.99   6.539%   $129.9669   $129.97   $129.95   $130.00  
  Purchase #3 $187.36   4.581%   $195.943   $195.94   $195.95   $195.90  
  Purchase #4 $13.95   12.153%   $15.6453   $15.65   $15.65   $15.60  
  Purchase #5 $54.83   5.758%   $57.9871   $57.99   $58.00   $58.00  
  Purchase #6 $65.31   6.565%   $69.5976   $69.60   $69.60   $69.60  
  Purchase #7 $163.76   7.716%   $176.3957   $176.40   $176.40   $176.40  
  7 purchase totals = $772.76       $818.4034   $818.42   $818.40   $818.40