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	$75.92	7.155%	$81.3521	$81.35	$81.35	$81.40
Purchase #2	$114.95	12.847%	$129.7176	$129.72	$129.70	$129.70
Purchase #3	$40.89	4.258%	$42.6311	$42.63	$42.65	$42.60
Purchase #4	$92.92	13.292%	$105.2709	$105.27	$105.25	$105.30
Purchase #5	$64.57	7.616%	$69.4877	$69.49	$69.50	$69.50
Purchase #6	$171.88	9.399%	$188.035	$188.04	$188.05	$188.00
Purchase #7	$35.48	5.250%	$37.3427	$37.34	$37.35	$37.30
7 purchase totals =	$596.61		$653.8371	$653.84	$653.85	$653.80