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 $162.61   13.595%   $184.7168   $184.72   $184.70   $184.70  
  Purchase #2 $184.55   5.841%   $195.3296   $195.33   $195.35   $195.30  
  Purchase #3 $28.56   6.220%   $30.3364   $30.34   $30.35   $30.30  
  Purchase #4 $51.62   10.472%   $57.0256   $57.03   $57.05   $57.00  
  Purchase #5 $51.48   4.607%   $53.8517   $53.85   $53.85   $53.90  
  Purchase #6 $206.77   6.291%   $219.7779   $219.78   $219.80   $219.80  
  Purchase #7 $65.57   5.539%   $69.2019   $69.20   $69.20   $69.20  
  7 purchase totals = $751.16       $810.2399   $810.25   $810.30   $810.20