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 $24.56   4.235%   $25.6001   $25.60   $25.60   $25.60  
  Purchase #2 $246.55   11.314%   $274.4447   $274.44   $274.45   $274.40  
  Purchase #3 $92.92   7.134%   $99.5489   $99.55   $99.55   $99.50  
  Purchase #4 $208.56   12.241%   $234.0898   $234.09   $234.10   $234.10  
  Purchase #5 $130.29   3.792%   $135.2306   $135.23   $135.25   $135.20  
  Purchase #6 $57.39   5.608%   $60.6084   $60.61   $60.60   $60.60  
  Purchase #7 $189.93   7.482%   $204.1406   $204.14   $204.15   $204.10  
  7 purchase totals = $950.20       $1,033.6631   $1,033.66   $1,033.70   $1,033.50