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 $60.57   6.418%   $64.4574   $64.46   $64.45   $64.50  
  Purchase #2 $163.57   5.550%   $172.6481   $172.65   $172.65   $172.60  
  Purchase #3 $126.90   5.862%   $134.3389   $134.34   $134.35   $134.30  
  Purchase #4 $44.99   10.705%   $49.8062   $49.81   $49.80   $49.80  
  Purchase #5 $149.31   10.294%   $164.68   $164.68   $164.70   $164.70  
  Purchase #6 $204.86   6.430%   $218.0325   $218.03   $218.05   $218.00  
  Purchase #7 $143.41   5.435%   $151.2043   $151.20   $151.20   $151.20  
  7 purchase totals = $893.61       $955.1674   $955.17   $955.20   $955.10