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 $60.83   6.310%   $64.6684   $64.67   $64.65   $64.70  
  Purchase #2 $238.80   13.793%   $271.7377   $271.74   $271.75   $271.70  
  Purchase #3 $190.27   6.136%   $201.945   $201.95   $201.95   $201.90  
  Purchase #4 $168.62   11.622%   $188.217   $188.22   $188.20   $188.20  
  Purchase #5 $61.85   8.425%   $67.0609   $67.06   $67.05   $67.10  
  Purchase #6 $250.54   10.352%   $276.4759   $276.48   $276.50   $276.50  
  Purchase #7 $248.28   10.159%   $273.5028   $273.50   $273.50   $273.50  
  7 purchase totals = $1,219.19       $1,343.6077   $1,343.62   $1,343.60   $1,343.60