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 $61.84   12.372%   $69.4908   $69.49   $69.50   $69.50  
  Purchase #2 $143.41   12.853%   $161.8425   $161.84   $161.85   $161.80  
  Purchase #3 $174.94   3.821%   $181.6245   $181.62   $181.60   $181.60  
  Purchase #4 $144.64   11.642%   $161.479   $161.48   $161.50   $161.50  
  Purchase #5 $10.95   10.624%   $12.1133   $12.11   $12.10   $12.10  
  Purchase #6 $158.49   5.212%   $166.7505   $166.75   $166.75   $166.80  
  Purchase #7 $20.86   13.551%   $23.6867   $23.69   $23.70   $23.70  
  7 purchase totals = $715.13       $776.9873   $776.98   $777.00   $777.00