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	$81.96	9.348%	$89.6216	$89.62	$89.60	$89.60
Purchase #2	$55.31	4.413%	$57.7508	$57.75	$57.75	$57.80
Purchase #3	$95.62	6.697%	$102.0237	$102.02	$102.00	$102.00
Purchase #4	$172.45	3.663%	$178.7668	$178.77	$178.75	$178.80
Purchase #5	$24.71	13.542%	$28.0562	$28.06	$28.05	$28.10
Purchase #6	$88.48	3.718%	$91.7697	$91.77	$91.75	$91.80
Purchase #7	$83.89	6.486%	$89.3311	$89.33	$89.35	$89.30
7 purchase totals =	$602.42		$637.3199	$637.32	$637.25	$637.40