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 $58.42   13.579%   $66.3529   $66.35   $66.35   $66.40  
  Purchase #2 $45.76   4.290%   $47.7231   $47.72   $47.70   $47.70  
  Purchase #3 $240.84   11.751%   $269.1411   $269.14   $269.15   $269.10  
  Purchase #4 $242.77   5.723%   $256.6637   $256.66   $256.65   $256.70  
  Purchase #5 $167.70   4.700%   $175.5819   $175.58   $175.60   $175.60  
  Purchase #6 $55.30   10.471%   $61.0905   $61.09   $61.10   $61.10  
  Purchase #7 $45.98   11.873%   $51.4392   $51.44   $51.45   $51.40  
  7 purchase totals = $856.77       $927.9924   $927.98   $928.00   $928.00