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 $151.75   11.794%   $169.6474   $169.65   $169.65   $169.60  
  Purchase #2 $113.40   7.784%   $122.2271   $122.23   $122.25   $122.20  
  Purchase #3 $145.26   13.691%   $165.1475   $165.15   $165.15   $165.10  
  Purchase #4 $228.60   12.661%   $257.543   $257.54   $257.55   $257.50  
  Purchase #5 $79.53   4.631%   $83.213   $83.21   $83.20   $83.20  
  Purchase #6 $44.95   6.613%   $47.9225   $47.92   $47.90   $47.90  
  Purchase #7 $15.61   3.596%   $16.1713   $16.17   $16.15   $16.20  
  7 purchase totals = $779.10       $861.8718   $861.87   $861.85   $861.70