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 $220.74   13.707%   $250.9968   $251.00   $251.00   $251.00  
  Purchase #2 $149.77   8.209%   $162.0646   $162.06   $162.05   $162.10  
  Purchase #3 $59.77   13.334%   $67.7397   $67.74   $67.75   $67.70  
  Purchase #4 $46.67   3.497%   $48.302   $48.30   $48.30   $48.30  
  Purchase #5 $71.52   13.723%   $81.3347   $81.33   $81.35   $81.30  
  Purchase #6 $190.61   5.193%   $200.5084   $200.51   $200.50   $200.50  
  Purchase #7 $194.54   13.730%   $221.2503   $221.25   $221.25   $221.30  
  7 purchase totals = $933.62       $1,032.1965   $1,032.19   $1,032.20   $1,032.20