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 $183.80   11.505%   $204.9462   $204.95   $204.95   $204.90  
  Purchase #2 $175.66   8.476%   $190.5489   $190.55   $190.55   $190.50  
  Purchase #3 $139.56   13.498%   $158.3978   $158.40   $158.40   $158.40  
  Purchase #4 $29.57   8.398%   $32.0533   $32.05   $32.05   $32.10  
  Purchase #5 $174.40   12.383%   $195.996   $196.00   $196.00   $196.00  
  Purchase #6 $22.30   4.616%   $23.3294   $23.33   $23.35   $23.30  
  Purchase #7 $158.45   11.579%   $176.7969   $176.80   $176.80   $176.80  
  7 purchase totals = $883.74       $982.0685   $982.08   $982.10   $982.00