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 $172.81   11.279%   $192.3012   $192.30   $192.30   $192.30  
  Purchase #2 $71.94   13.537%   $81.6785   $81.68   $81.70   $81.70  
  Purchase #3 $19.46   11.787%   $21.7538   $21.75   $21.75   $21.80  
  Purchase #4 $27.84   8.770%   $30.2816   $30.28   $30.30   $30.30  
  Purchase #5 $50.47   9.409%   $55.2187   $55.22   $55.20   $55.20  
  Purchase #6 $237.88   9.520%   $260.5262   $260.53   $260.55   $260.50  
  Purchase #7 $160.76   9.164%   $175.492   $175.49   $175.50   $175.50  
  7 purchase totals = $741.16       $817.2520   $817.25   $817.30   $817.30