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	$12.41	6.488%	$13.2152	$13.22	$13.20	$13.20
Purchase #2	$245.37	9.598%	$268.9206	$268.92	$268.90	$268.90
Purchase #3	$159.76	4.429%	$166.8358	$166.84	$166.85	$166.80
Purchase #4	$62.36	8.690%	$67.7791	$67.78	$67.80	$67.80
Purchase #5	$174.58	9.375%	$190.9469	$190.95	$190.95	$190.90
Purchase #6	$118.81	8.829%	$129.2997	$129.30	$129.30	$129.30
Purchase #7	$196.57	11.350%	$218.8807	$218.88	$218.90	$218.90
7 purchase totals =	$969.86		$1,055.8780	$1,055.89	$1,055.90	$1,055.80