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	$67.57	5.127%	$71.0343	$71.03	$71.05	$71.00
Purchase #2	$143.76	5.515%	$151.6884	$151.69	$151.70	$151.70
Purchase #3	$88.92	10.361%	$98.133	$98.13	$98.15	$98.10
Purchase #4	$50.49	9.320%	$55.1957	$55.20	$55.20	$55.20
Purchase #5	$35.63	8.539%	$38.6724	$38.67	$38.65	$38.70
Purchase #6	$85.89	5.642%	$90.7359	$90.74	$90.75	$90.70
Purchase #7	$30.59	12.778%	$34.4988	$34.50	$34.50	$34.50
7 purchase totals =	$502.85		$539.9585	$539.96	$540.00	$539.90