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 $32.82   11.468%   $36.5838   $36.58   $36.60   $36.60  
  Purchase #2 $109.71   3.310%   $113.3414   $113.34   $113.35   $113.30  
  Purchase #3 $27.26   4.750%   $28.5549   $28.55   $28.55   $28.60  
  Purchase #4 $224.80   3.492%   $232.65   $232.65   $232.65   $232.70  
  Purchase #5 $248.90   5.336%   $262.1813   $262.18   $262.20   $262.20  
  Purchase #6 $204.27   5.180%   $214.8512   $214.85   $214.85   $214.90  
  Purchase #7 $87.54   7.379%   $93.9996   $94.00   $94.00   $94.00  
  7 purchase totals = $935.30       $982.1622   $982.15   $982.20   $982.30