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 $166.64   10.569%   $184.2522   $184.25   $184.25   $184.30  
  Purchase #2 $204.26   13.849%   $232.548   $232.55   $232.55   $232.50  
  Purchase #3 $54.62   13.624%   $62.0614   $62.06   $62.05   $62.10  
  Purchase #4 $239.62   9.583%   $262.5828   $262.58   $262.60   $262.60  
  Purchase #5 $45.60   7.263%   $48.9119   $48.91   $48.90   $48.90  
  Purchase #6 $209.75   3.287%   $216.6445   $216.64   $216.65   $216.60  
  Purchase #7 $126.48   6.439%   $134.624   $134.62   $134.60   $134.60  
  7 purchase totals = $1,046.97       $1,141.6248   $1,141.61   $1,141.60   $1,141.60