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 $56.75   13.222%   $64.2535   $64.25   $64.25   $64.30  
  Purchase #2 $57.93   3.566%   $59.9958   $60.00   $60.00   $60.00  
  Purchase #3 $213.30   8.723%   $231.9062   $231.91   $231.90   $231.90  
  Purchase #4 $193.76   7.570%   $208.4276   $208.43   $208.45   $208.40  
  Purchase #5 $172.97   7.276%   $185.5553   $185.56   $185.55   $185.60  
  Purchase #6 $208.59   10.671%   $230.8486   $230.85   $230.85   $230.80  
  Purchase #7 $24.29   9.724%   $26.652   $26.65   $26.65   $26.70  
  7 purchase totals = $927.59       $1,007.6390   $1,007.65   $1,007.65   $1,007.70