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 $117.96   4.623%   $123.4133   $123.41   $123.40   $123.40  
  Purchase #2 $80.72   7.486%   $86.7627   $86.76   $86.75   $86.80  
  Purchase #3 $106.52   11.665%   $118.9456   $118.95   $118.95   $118.90  
  Purchase #4 $139.98   9.369%   $153.0947   $153.09   $153.10   $153.10  
  Purchase #5 $219.79   11.445%   $244.945   $244.95   $244.95   $244.90  
  Purchase #6 $115.36   8.474%   $125.1356   $125.14   $125.15   $125.10  
  Purchase #7 $102.81   8.112%   $111.1499   $111.15   $111.15   $111.10  
  7 purchase totals = $883.14       $963.4468   $963.45   $963.45   $963.30