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 $149.51   13.572%   $169.8015   $169.80   $169.80   $169.80  
  Purchase #2 $187.91   4.272%   $195.9375   $195.94   $195.95   $195.90  
  Purchase #3 $70.55   6.652%   $75.243   $75.24   $75.25   $75.20  
  Purchase #4 $77.66   8.863%   $84.543   $84.54   $84.55   $84.50  
  Purchase #5 $222.81   11.167%   $247.6912   $247.69   $247.70   $247.70  
  Purchase #6 $154.58   8.539%   $167.7796   $167.78   $167.80   $167.80  
  Purchase #7 $131.77   8.133%   $142.4869   $142.49   $142.50   $142.50  
  7 purchase totals = $994.79       $1,083.4827   $1,083.48   $1,083.55   $1,083.40