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 $43.97   10.577%   $48.6207   $48.62   $48.60   $48.60  
  Purchase #2 $44.88   11.120%   $49.8707   $49.87   $49.85   $49.90  
  Purchase #3 $151.74   11.270%   $168.8411   $168.84   $168.85   $168.80  
  Purchase #4 $118.92   10.562%   $131.4803   $131.48   $131.50   $131.50  
  Purchase #5 $77.63   10.349%   $85.6639   $85.66   $85.65   $85.70  
  Purchase #6 $232.32   10.835%   $257.4919   $257.49   $257.50   $257.50  
  Purchase #7 $175.84   5.555%   $185.6079   $185.61   $185.60   $185.60  
  7 purchase totals = $845.30       $927.5765   $927.57   $927.55   $927.60