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 $211.62   10.272%   $233.3576   $233.36   $233.35   $233.40  
  Purchase #2 $150.85   5.540%   $159.2071   $159.21   $159.20   $159.20  
  Purchase #3 $43.46   3.602%   $45.0254   $45.03   $45.05   $45.00  
  Purchase #4 $99.96   5.716%   $105.6737   $105.67   $105.65   $105.70  
  Purchase #5 $106.84   5.431%   $112.6425   $112.64   $112.65   $112.60  
  Purchase #6 $61.54   10.329%   $67.8965   $67.90   $67.90   $67.90  
  Purchase #7 $197.38   4.305%   $205.8772   $205.88   $205.90   $205.90  
  7 purchase totals = $871.65       $929.6800   $929.69   $929.70   $929.70