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 $41.41   11.127%   $46.0177   $46.02   $46.00   $46.00  
  Purchase #2 $74.30   11.355%   $82.7368   $82.74   $82.75   $82.70  
  Purchase #3 $219.74   12.615%   $247.4602   $247.46   $247.45   $247.50  
  Purchase #4 $190.52   9.326%   $208.2879   $208.29   $208.30   $208.30  
  Purchase #5 $87.83   13.560%   $99.7397   $99.74   $99.75   $99.70  
  Purchase #6 $64.35   11.780%   $71.9304   $71.93   $71.95   $71.90  
  Purchase #7 $214.26   11.757%   $239.4505   $239.45   $239.45   $239.50  
  7 purchase totals = $892.41       $995.6232   $995.63   $995.65   $995.60