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 $140.87   7.858%   $151.9396   $151.94   $151.95   $151.90  
  Purchase #2 $86.57   10.631%   $95.7733   $95.77   $95.75   $95.80  
  Purchase #3 $210.83   8.495%   $228.74   $228.74   $228.75   $228.70  
  Purchase #4 $130.37   8.813%   $141.8595   $141.86   $141.85   $141.90  
  Purchase #5 $30.61   10.696%   $33.884   $33.88   $33.90   $33.90  
  Purchase #6 $165.67   12.661%   $186.6455   $186.65   $186.65   $186.60  
  Purchase #7 $13.62   6.435%   $14.4964   $14.50   $14.50   $14.50  
  7 purchase totals = $778.54       $853.3383   $853.34   $853.35   $853.30