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 $62.97   11.121%   $69.9729   $69.97   $69.95   $70.00  
  Purchase #2 $212.99   11.820%   $238.1654   $238.17   $238.15   $238.20  
  Purchase #3 $31.73   12.294%   $35.6309   $35.63   $35.65   $35.60  
  Purchase #4 $198.48   7.108%   $212.588   $212.59   $212.60   $212.60  
  Purchase #5 $58.83   3.258%   $60.7467   $60.75   $60.75   $60.70  
  Purchase #6 $31.35   10.481%   $34.6358   $34.64   $34.65   $34.60  
  Purchase #7 $116.41   8.423%   $126.2152   $126.22   $126.20   $126.20  
  7 purchase totals = $712.76       $777.9549   $777.97   $777.95   $777.90