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 $81.58   5.683%   $86.2162   $86.22   $86.20   $86.20  
  Purchase #2 $198.84   10.114%   $218.9507   $218.95   $218.95   $219.00  
  Purchase #3 $23.37   5.396%   $24.631   $24.63   $24.65   $24.60  
  Purchase #4 $108.38   5.595%   $114.4439   $114.44   $114.45   $114.40  
  Purchase #5 $164.66   5.785%   $174.1856   $174.19   $174.20   $174.20  
  Purchase #6 $206.32   11.787%   $230.6389   $230.64   $230.65   $230.60  
  Purchase #7 $27.43   5.761%   $29.0102   $29.01   $29.00   $29.00  
  7 purchase totals = $810.58       $878.0765   $878.08   $878.10   $878.00