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 $214.94   8.392%   $232.9778   $232.98   $233.00   $233.00  
  Purchase #2 $219.84   8.826%   $239.2431   $239.24   $239.25   $239.20  
  Purchase #3 $29.48   11.455%   $32.8569   $32.86   $32.85   $32.90  
  Purchase #4 $56.50   11.365%   $62.9212   $62.92   $62.90   $62.90  
  Purchase #5 $14.33   7.742%   $15.4394   $15.44   $15.45   $15.40  
  Purchase #6 $17.57   4.606%   $18.3793   $18.38   $18.40   $18.40  
  Purchase #7 $64.28   8.666%   $69.8505   $69.85   $69.85   $69.90  
  7 purchase totals = $616.94       $671.6682   $671.67   $671.70   $671.70