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 $176.82   8.487%   $191.8267   $191.83   $191.85   $191.80  
  Purchase #2 $213.87   4.671%   $223.8599   $223.86   $223.85   $223.90  
  Purchase #3 $197.73   8.361%   $214.2622   $214.26   $214.25   $214.30  
  Purchase #4 $58.45   7.384%   $62.7659   $62.77   $62.75   $62.80  
  Purchase #5 $171.58   11.241%   $190.8673   $190.87   $190.85   $190.90  
  Purchase #6 $168.75   8.404%   $182.9318   $182.93   $182.95   $182.90  
  Purchase #7 $141.79   13.559%   $161.0153   $161.02   $161.00   $161.00  
  7 purchase totals = $1,128.99       $1,227.5291   $1,227.54   $1,227.50   $1,227.60