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	$250.30	4.601%	$261.8163	$261.82	$261.80	$261.80
Purchase #2	$76.48	7.856%	$82.4883	$82.49	$82.50	$82.50
Purchase #3	$188.92	7.569%	$203.2194	$203.22	$203.20	$203.20
Purchase #4	$55.66	6.507%	$59.2818	$59.28	$59.30	$59.30
Purchase #5	$95.55	12.530%	$107.5224	$107.52	$107.50	$107.50
Purchase #6	$83.89	5.202%	$88.254	$88.25	$88.25	$88.30
Purchase #7	$98.41	6.407%	$104.7151	$104.72	$104.70	$104.70
7 purchase totals =	$849.21		$907.2973	$907.30	$907.25	$907.30