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 $209.33   11.788%   $234.0058   $234.01   $234.00   $234.00  
  Purchase #2 $106.40   11.699%   $118.8477   $118.85   $118.85   $118.80  
  Purchase #3 $156.91   12.433%   $176.4186   $176.42   $176.40   $176.40  
  Purchase #4 $137.63   13.359%   $156.016   $156.02   $156.00   $156.00  
  Purchase #5 $64.89   12.807%   $73.2005   $73.20   $73.20   $73.20  
  Purchase #6 $139.30   11.665%   $155.5493   $155.55   $155.55   $155.50  
  Purchase #7 $115.25   7.830%   $124.2741   $124.27   $124.25   $124.30  
  7 purchase totals = $929.71       $1,038.3120   $1,038.32   $1,038.25   $1,038.20