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	$79.94	11.741%	$89.3258	$89.33	$89.35	$89.30
Purchase #2	$192.30	12.199%	$215.7587	$215.76	$215.75	$215.80
Purchase #3	$221.94	8.640%	$241.1156	$241.12	$241.10	$241.10
Purchase #4	$118.68	8.541%	$128.8165	$128.82	$128.80	$128.80
Purchase #5	$249.46	13.112%	$282.1692	$282.17	$282.15	$282.20
Purchase #6	$107.71	8.825%	$117.2154	$117.22	$117.20	$117.20
Purchase #7	$137.69	11.768%	$153.8934	$153.89	$153.90	$153.90
7 purchase totals =	$1,107.72		$1,228.2946	$1,228.31	$1,228.25	$1,228.30