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 $87.48   9.828%   $96.0775   $96.08   $96.10   $96.10  
  Purchase #2 $122.38   11.358%   $136.2799   $136.28   $136.30   $136.30  
  Purchase #3 $81.47   12.323%   $91.5095   $91.51   $91.50   $91.50  
  Purchase #4 $228.58   3.313%   $236.1529   $236.15   $236.15   $236.20  
  Purchase #5 $29.28   13.753%   $33.3069   $33.31   $33.30   $33.30  
  Purchase #6 $72.41   6.216%   $76.911   $76.91   $76.90   $76.90  
  Purchase #7 $186.46   11.768%   $208.4026   $208.40   $208.40   $208.40  
  7 purchase totals = $808.06       $878.6403   $878.64   $878.65   $878.70