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	$199.92	11.144%	$222.1991	$222.20	$222.20	$222.20
Purchase #2	$79.79	3.160%	$82.3114	$82.31	$82.30	$82.30
Purchase #3	$239.62	3.424%	$247.8246	$247.82	$247.80	$247.80
Purchase #4	$41.36	10.135%	$45.5518	$45.55	$45.55	$45.60
Purchase #5	$159.71	9.536%	$174.9399	$174.94	$174.95	$174.90
Purchase #6	$80.51	10.828%	$89.2276	$89.23	$89.25	$89.20
Purchase #7	$116.57	11.362%	$129.8147	$129.81	$129.80	$129.80
7 purchase totals =	$917.48		$991.8691	$991.86	$991.85	$991.80