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 $218.90   3.397%   $226.336   $226.34   $226.35   $226.30  
  Purchase #2 $128.79   4.332%   $134.3692   $134.37   $134.35   $134.40  
  Purchase #3 $21.48   5.719%   $22.7084   $22.71   $22.70   $22.70  
  Purchase #4 $14.27   7.292%   $15.3106   $15.31   $15.30   $15.30  
  Purchase #5 $59.26   11.136%   $65.8592   $65.86   $65.85   $65.90  
  Purchase #6 $44.78   9.814%   $49.1747   $49.17   $49.15   $49.20  
  Purchase #7 $211.45   4.623%   $221.2253   $221.23   $221.25   $221.20  
  7 purchase totals = $698.93       $734.9834   $734.99   $734.95   $735.00