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	$154.78	10.869%	$171.603	$171.60	$171.60	$171.60
Purchase #2	$79.71	12.166%	$89.4075	$89.41	$89.40	$89.40
Purchase #3	$13.50	3.797%	$14.0126	$14.01	$14.00	$14.00
Purchase #4	$173.81	9.466%	$190.2629	$190.26	$190.25	$190.30
Purchase #5	$188.52	11.666%	$210.5127	$210.51	$210.50	$210.50
Purchase #6	$98.76	10.502%	$109.1318	$109.13	$109.15	$109.10
Purchase #7	$88.27	5.228%	$92.8848	$92.88	$92.90	$92.90
7 purchase totals =	$797.35		$877.8153	$877.80	$877.80	$877.80