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	$51.36	11.265%	$57.1457	$57.15	$57.15	$57.10
Purchase #2	$202.38	13.521%	$229.7438	$229.74	$229.75	$229.70
Purchase #3	$81.63	7.688%	$87.9057	$87.91	$87.90	$87.90
Purchase #4	$51.27	11.275%	$57.0507	$57.05	$57.05	$57.10
Purchase #5	$145.38	4.741%	$152.2725	$152.27	$152.25	$152.30
Purchase #6	$229.67	10.199%	$253.094	$253.09	$253.10	$253.10
Purchase #7	$86.31	3.601%	$89.418	$89.42	$89.40	$89.40
7 purchase totals =	$848.00		$926.6304	$926.63	$926.60	$926.60