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	$177.74	3.178%	$183.3886	$183.39	$183.40	$183.40
Purchase #2	$73.58	6.646%	$78.4701	$78.47	$78.45	$78.50
Purchase #3	$104.56	3.440%	$108.1569	$108.16	$108.15	$108.20
Purchase #4	$171.59	6.829%	$183.3079	$183.31	$183.30	$183.30
Purchase #5	$45.43	13.841%	$51.718	$51.72	$51.70	$51.70
Purchase #6	$81.28	10.468%	$89.7884	$89.79	$89.80	$89.80
Purchase #7	$98.50	11.640%	$109.9654	$109.97	$109.95	$110.00
7 purchase totals =	$752.68		$804.7953	$804.81	$804.75	$804.90