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 $57.72   4.695%   $60.43   $60.43   $60.45   $60.40  
  Purchase #2 $161.89   13.447%   $183.6593   $183.66   $183.65   $183.70  
  Purchase #3 $74.77   3.557%   $77.4296   $77.43   $77.45   $77.40  
  Purchase #4 $203.99   3.471%   $211.0705   $211.07   $211.05   $211.10  
  Purchase #5 $23.27   5.783%   $24.6157   $24.62   $24.60   $24.60  
  Purchase #6 $246.53   6.532%   $262.6333   $262.63   $262.65   $262.60  
  Purchase #7 $142.78   3.178%   $147.3175   $147.32   $147.30   $147.30  
  7 purchase totals = $910.95       $967.1559   $967.16   $967.15   $967.10