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 $156.87   5.539%   $165.559   $165.56   $165.55   $165.60  
  Purchase #2 $47.48   7.552%   $51.0657   $51.07   $51.05   $51.10  
  Purchase #3 $144.61   9.663%   $158.5837   $158.58   $158.60   $158.60  
  Purchase #4 $205.35   11.349%   $228.6552   $228.66   $228.65   $228.70  
  Purchase #5 $198.85   8.432%   $215.617   $215.62   $215.60   $215.60  
  Purchase #6 $16.62   5.599%   $17.5506   $17.55   $17.55   $17.60  
  Purchase #7 $57.67   6.286%   $61.2951   $61.30   $61.30   $61.30  
  7 purchase totals = $827.45       $898.3263   $898.34   $898.30   $898.50