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 $211.55   11.797%   $236.5066   $236.51   $236.50   $236.50  
  Purchase #2 $21.81   11.134%   $24.2383   $24.24   $24.25   $24.20  
  Purchase #3 $136.39   13.496%   $154.7972   $154.80   $154.80   $154.80  
  Purchase #4 $217.52   6.482%   $231.6196   $231.62   $231.60   $231.60  
  Purchase #5 $5.61   3.147%   $5.7865   $5.79   $5.80   $5.80  
  Purchase #6 $186.89   12.409%   $210.0812   $210.08   $210.10   $210.10  
  Purchase #7 $230.70   13.299%   $261.3808   $261.38   $261.40   $261.40  
  7 purchase totals = $1,010.47       $1,124.4102   $1,124.42   $1,124.45   $1,124.40