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 $228.49   8.429%   $247.7494   $247.75   $247.75   $247.70  
  Purchase #2 $65.49   3.851%   $68.012   $68.01   $68.00   $68.00  
  Purchase #3 $177.91   3.244%   $183.6814   $183.68   $183.70   $183.70  
  Purchase #4 $93.64   10.560%   $103.5284   $103.53   $103.55   $103.50  
  Purchase #5 $53.62   3.431%   $55.4597   $55.46   $55.45   $55.50  
  Purchase #6 $203.31   9.393%   $222.4069   $222.41   $222.40   $222.40  
  Purchase #7 $176.88   5.842%   $187.2133   $187.21   $187.20   $187.20  
  7 purchase totals = $999.34       $1,068.0511   $1,068.05   $1,068.05   $1,068.00