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 $92.50   4.695%   $96.8429   $96.84   $96.85   $96.80  
  Purchase #2 $17.50   12.299%   $19.6523   $19.65   $19.65   $19.70  
  Purchase #3 $202.69   13.517%   $230.0876   $230.09   $230.10   $230.10  
  Purchase #4 $143.81   9.137%   $156.9499   $156.95   $156.95   $156.90  
  Purchase #5 $190.26   9.461%   $208.2605   $208.26   $208.25   $208.30  
  Purchase #6 $107.93   8.155%   $116.7317   $116.73   $116.75   $116.70  
  Purchase #7 $174.75   11.589%   $195.0018   $195.00   $195.00   $195.00  
  7 purchase totals = $929.44       $1,023.5267   $1,023.52   $1,023.55   $1,023.50