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 $204.91   11.390%   $228.2492   $228.25   $228.25   $228.20  
  Purchase #2 $54.75   8.589%   $59.4525   $59.45   $59.45   $59.50  
  Purchase #3 $190.51   3.326%   $196.8464   $196.85   $196.85   $196.80  
  Purchase #4 $151.72   7.613%   $163.2704   $163.27   $163.25   $163.30  
  Purchase #5 $21.46   10.192%   $23.6472   $23.65   $23.65   $23.60  
  Purchase #6 $94.67   12.286%   $106.3012   $106.30   $106.30   $106.30  
  Purchase #7 $27.52   10.515%   $30.4137   $30.41   $30.40   $30.40  
  7 purchase totals = $745.54       $808.1806   $808.18   $808.15   $808.10