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	$77.62	8.167%	$83.9592	$83.96	$83.95	$84.00
Purchase #2	$52.64	13.684%	$59.8433	$59.84	$59.85	$59.80
Purchase #3	$54.65	8.670%	$59.3882	$59.39	$59.40	$59.40
Purchase #4	$233.27	13.279%	$264.2459	$264.25	$264.25	$264.20
Purchase #5	$90.38	8.656%	$98.2033	$98.20	$98.20	$98.20
Purchase #6	$31.76	9.333%	$34.7242	$34.72	$34.70	$34.70
Purchase #7	$131.35	12.278%	$147.4772	$147.48	$147.50	$147.50
7 purchase totals =	$671.67		$747.8413	$747.84	$747.85	$747.80