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 $146.65   3.607%   $151.9397   $151.94   $151.95   $151.90  
  Purchase #2 $17.66   5.390%   $18.6119   $18.61   $18.60   $18.60  
  Purchase #3 $180.35   3.316%   $186.3304   $186.33   $186.35   $186.30  
  Purchase #4 $82.44   5.208%   $86.7335   $86.73   $86.75   $86.70  
  Purchase #5 $234.83   8.359%   $254.4594   $254.46   $254.45   $254.50  
  Purchase #6 $5.91   5.638%   $6.2432   $6.24   $6.25   $6.20  
  Purchase #7 $209.99   4.359%   $219.1435   $219.14   $219.15   $219.10  
  7 purchase totals = $877.83       $923.4616   $923.45   $923.50   $923.30