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 $61.41   6.317%   $65.2893   $65.29   $65.30   $65.30  
  Purchase #2 $139.95   11.792%   $156.4529   $156.45   $156.45   $156.50  
  Purchase #3 $9.45   13.627%   $10.7378   $10.74   $10.75   $10.70  
  Purchase #4 $161.42   9.746%   $177.152   $177.15   $177.15   $177.20  
  Purchase #5 $157.77   6.624%   $168.2207   $168.22   $168.20   $168.20  
  Purchase #6 $169.42   13.570%   $192.4103   $192.41   $192.40   $192.40  
  Purchase #7 $232.83   11.542%   $259.7032   $259.70   $259.70   $259.70  
  7 purchase totals = $932.25       $1,029.9662   $1,029.96   $1,029.95   $1,030.00