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 $183.58   12.720%   $206.9314   $206.93   $206.95   $206.90  
  Purchase #2 $14.29   4.124%   $14.8793   $14.88   $14.90   $14.90  
  Purchase #3 $245.49   3.505%   $254.0944   $254.09   $254.10   $254.10  
  Purchase #4 $25.75   9.756%   $28.2622   $28.26   $28.25   $28.30  
  Purchase #5 $195.48   11.595%   $218.1459   $218.15   $218.15   $218.10  
  Purchase #6 $193.30   11.434%   $215.4019   $215.40   $215.40   $215.40  
  Purchase #7 $171.52   6.435%   $182.5573   $182.56   $182.55   $182.60  
  7 purchase totals = $1,029.41       $1,120.2724   $1,120.27   $1,120.30   $1,120.30