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 $214.47   8.298%   $232.2667   $232.27   $232.25   $232.30  
  Purchase #2 $246.35   13.350%   $279.2377   $279.24   $279.25   $279.20  
  Purchase #3 $219.51   4.358%   $229.0762   $229.08   $229.10   $229.10  
  Purchase #4 $26.44   3.345%   $27.3244   $27.32   $27.30   $27.30  
  Purchase #5 $71.27   4.597%   $74.5463   $74.55   $74.55   $74.50  
  Purchase #6 $236.39   12.184%   $265.1918   $265.19   $265.20   $265.20  
  Purchase #7 $94.25   7.225%   $101.0596   $101.06   $101.05   $101.10  
  7 purchase totals = $1,108.68       $1,208.7027   $1,208.71   $1,208.70   $1,208.70