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	$172.64	10.515%	$190.7931	$190.79	$190.80	$190.80
Purchase #2	$154.44	6.550%	$164.5558	$164.56	$164.55	$164.60
Purchase #3	$55.92	12.470%	$62.8932	$62.89	$62.90	$62.90
Purchase #4	$233.78	6.850%	$249.7939	$249.79	$249.80	$249.80
Purchase #5	$236.78	3.554%	$245.1952	$245.20	$245.20	$245.20
Purchase #6	$17.64	4.802%	$18.4871	$18.49	$18.50	$18.50
Purchase #7	$39.31	3.605%	$40.7271	$40.73	$40.75	$40.70
7 purchase totals =	$910.51		$972.4454	$972.45	$972.50	$972.50