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	$107.52	12.791%	$121.2729	$121.27	$121.25	$121.30
Purchase #2	$209.64	3.127%	$216.1954	$216.20	$216.20	$216.20
Purchase #3	$123.84	10.738%	$137.1379	$137.14	$137.15	$137.10
Purchase #4	$191.90	3.341%	$198.3114	$198.31	$198.30	$198.30
Purchase #5	$50.43	6.865%	$53.892	$53.89	$53.90	$53.90
Purchase #6	$88.63	7.511%	$95.287	$95.29	$95.30	$95.30
Purchase #7	$186.92	3.836%	$194.0903	$194.09	$194.10	$194.10
7 purchase totals =	$958.88		$1,016.1869	$1,016.19	$1,016.20	$1,016.20