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 $147.85   10.361%   $163.1687   $163.17   $163.15   $163.20  
  Purchase #2 $135.76   5.575%   $143.3286   $143.33   $143.35   $143.30  
  Purchase #3 $56.90   11.326%   $63.3445   $63.34   $63.35   $63.30  
  Purchase #4 $241.58   4.567%   $252.613   $252.61   $252.60   $252.60  
  Purchase #5 $11.99   3.498%   $12.4094   $12.41   $12.40   $12.40  
  Purchase #6 $171.75   4.663%   $179.7587   $179.76   $179.75   $179.80  
  Purchase #7 $136.59   8.393%   $148.054   $148.05   $148.05   $148.10  
  7 purchase totals = $902.42       $962.6769   $962.67   $962.65   $962.70