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 $56.70   13.141%   $64.1509   $64.15   $64.15   $64.20  
  Purchase #2 $62.69   4.268%   $65.3656   $65.37   $65.35   $65.40  
  Purchase #3 $232.65   13.323%   $263.646   $263.65   $263.65   $263.60  
  Purchase #4 $185.62   12.359%   $208.5608   $208.56   $208.55   $208.60  
  Purchase #5 $16.51   3.536%   $17.0938   $17.09   $17.10   $17.10  
  Purchase #6 $54.86   3.506%   $56.7834   $56.78   $56.80   $56.80  
  Purchase #7 $70.94   13.793%   $80.7248   $80.72   $80.70   $80.70  
  7 purchase totals = $679.97       $756.3253   $756.32   $756.30   $756.40