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	$40.59	3.605%	$42.0533	$42.05	$42.05	$42.10
Purchase #2	$85.48	12.715%	$96.3488	$96.35	$96.35	$96.30
Purchase #3	$56.41	10.633%	$62.4081	$62.41	$62.40	$62.40
Purchase #4	$125.53	13.833%	$142.8946	$142.89	$142.90	$142.90
Purchase #5	$142.89	8.482%	$155.0099	$155.01	$155.00	$155.00
Purchase #6	$108.58	5.416%	$114.4607	$114.46	$114.45	$114.50
Purchase #7	$173.61	3.513%	$179.7089	$179.71	$179.70	$179.70
7 purchase totals =	$733.09		$792.8843	$792.88	$792.85	$792.90