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 $226.45   8.872%   $246.5406   $246.54   $246.55   $246.50  
  Purchase #2 $20.35   4.414%   $21.2482   $21.25   $21.25   $21.20  
  Purchase #3 $69.83   5.301%   $73.5317   $73.53   $73.55   $73.50  
  Purchase #4 $99.60   6.424%   $105.9983   $106.00   $106.00   $106.00  
  Purchase #5 $230.70   10.171%   $254.1645   $254.16   $254.15   $254.20  
  Purchase #6 $59.89   10.613%   $66.2461   $66.25   $66.25   $66.20  
  Purchase #7 $246.68   6.133%   $261.8089   $261.81   $261.80   $261.80  
  7 purchase totals = $953.50       $1,029.5383   $1,029.54   $1,029.55   $1,029.40