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	$167.85	13.732%	$190.8992	$190.90	$190.90	$190.90
Purchase #2	$141.57	6.150%	$150.2766	$150.28	$150.30	$150.30
Purchase #3	$141.50	13.112%	$160.0535	$160.05	$160.05	$160.10
Purchase #4	$108.73	3.124%	$112.1267	$112.13	$112.15	$112.10
Purchase #5	$42.79	3.427%	$44.2564	$44.26	$44.25	$44.30
Purchase #6	$56.80	4.279%	$59.2305	$59.23	$59.25	$59.20
Purchase #7	$158.38	6.623%	$168.8695	$168.87	$168.85	$168.90
7 purchase totals =	$817.62		$885.7124	$885.72	$885.75	$885.80