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	$93.98	7.393%	$100.9279	$100.93	$100.95	$100.90
Purchase #2	$33.75	4.591%	$35.2995	$35.30	$35.30	$35.30
Purchase #3	$62.89	10.522%	$69.5073	$69.51	$69.50	$69.50
Purchase #4	$160.48	11.253%	$178.5388	$178.54	$178.55	$178.50
Purchase #5	$20.81	5.256%	$21.9038	$21.90	$21.90	$21.90
Purchase #6	$106.40	13.122%	$120.3618	$120.36	$120.35	$120.40
Purchase #7	$142.51	13.784%	$162.1536	$162.15	$162.15	$162.20
7 purchase totals =	$620.82		$688.6927	$688.69	$688.70	$688.70