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	$72.40	7.573%	$77.8829	$77.88	$77.90	$77.90
Purchase #2	$121.31	12.132%	$136.0273	$136.03	$136.05	$136.00
Purchase #3	$32.29	7.810%	$34.8118	$34.81	$34.80	$34.80
Purchase #4	$92.71	8.567%	$100.6525	$100.65	$100.65	$100.70
Purchase #5	$30.46	11.201%	$33.8718	$33.87	$33.85	$33.90
Purchase #6	$71.99	8.787%	$78.3158	$78.32	$78.30	$78.30
Purchase #7	$142.74	3.107%	$147.1749	$147.17	$147.15	$147.20
7 purchase totals =	$563.90		$608.7370	$608.73	$608.70	$608.80