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 $150.57   9.368%   $164.6754   $164.68   $164.70   $164.70  
  Purchase #2 $180.34   3.118%   $185.963   $185.96   $185.95   $186.00  
  Purchase #3 $56.33   13.671%   $64.0309   $64.03   $64.05   $64.00  
  Purchase #4 $184.42   9.653%   $202.2221   $202.22   $202.20   $202.20  
  Purchase #5 $70.29   13.624%   $79.8663   $79.87   $79.85   $79.90  
  Purchase #6 $61.63   8.437%   $66.8297   $66.83   $66.85   $66.80  
  Purchase #7 $238.35   8.781%   $259.2795   $259.28   $259.30   $259.30  
  7 purchase totals = $941.93       $1,022.8669   $1,022.87   $1,022.90   $1,022.90