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 $183.70   12.108%   $205.9424   $205.94   $205.95   $205.90  
  Purchase #2 $72.55   9.244%   $79.2565   $79.26   $79.25   $79.30  
  Purchase #3 $246.74   5.260%   $259.7185   $259.72   $259.70   $259.70  
  Purchase #4 $67.46   11.121%   $74.9622   $74.96   $74.95   $75.00  
  Purchase #5 $110.36   6.397%   $117.4197   $117.42   $117.40   $117.40  
  Purchase #6 $45.51   7.245%   $48.8072   $48.81   $48.80   $48.80  
  Purchase #7 $130.43   7.544%   $140.2696   $140.27   $140.25   $140.30  
  7 purchase totals = $856.75       $926.3761   $926.38   $926.30   $926.40