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 $91.37   4.641%   $95.6105   $95.61   $95.60   $95.60  
  Purchase #2 $182.50   6.227%   $193.8643   $193.86   $193.85   $193.90  
  Purchase #3 $174.89   10.294%   $192.8932   $192.89   $192.90   $192.90  
  Purchase #4 $168.59   10.363%   $186.061   $186.06   $186.05   $186.10  
  Purchase #5 $99.80   5.831%   $105.6193   $105.62   $105.60   $105.60  
  Purchase #6 $112.67   7.759%   $121.4121   $121.41   $121.40   $121.40  
  Purchase #7 $61.29   6.618%   $65.3462   $65.35   $65.35   $65.30  
  7 purchase totals = $891.11       $960.8066   $960.80   $960.75   $960.80