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 $55.57   10.421%   $61.3609   $61.36   $61.35   $61.40  
  Purchase #2 $217.79   8.870%   $237.108   $237.11   $237.10   $237.10  
  Purchase #3 $79.95   8.388%   $86.6562   $86.66   $86.65   $86.70  
  Purchase #4 $195.45   3.315%   $201.9292   $201.93   $201.95   $201.90  
  Purchase #5 $56.25   5.523%   $59.3567   $59.36   $59.35   $59.40  
  Purchase #6 $153.56   13.482%   $174.263   $174.26   $174.25   $174.30  
  Purchase #7 $13.31   8.752%   $14.4749   $14.47   $14.45   $14.50  
  7 purchase totals = $771.88       $835.1489   $835.15   $835.10   $835.30