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 $214.52   12.852%   $242.0901   $242.09   $242.10   $242.10  
  Purchase #2 $82.49   13.394%   $93.5387   $93.54   $93.55   $93.50  
  Purchase #3 $246.91   6.359%   $262.611   $262.61   $262.60   $262.60  
  Purchase #4 $160.99   6.434%   $171.3481   $171.35   $171.35   $171.30  
  Purchase #5 $107.32   5.599%   $113.3288   $113.33   $113.35   $113.30  
  Purchase #6 $13.64   5.130%   $14.3397   $14.34   $14.35   $14.30  
  Purchase #7 $244.80   6.605%   $260.969   $260.97   $260.95   $261.00  
  7 purchase totals = $1,070.67       $1,158.2254   $1,158.23   $1,158.25   $1,158.10