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	$147.51	10.537%	$163.0531	$163.05	$163.05	$163.10
Purchase #2	$44.32	3.388%	$45.8216	$45.82	$45.80	$45.80
Purchase #3	$161.36	6.507%	$171.8597	$171.86	$171.85	$171.90
Purchase #4	$152.67	12.665%	$172.0057	$172.01	$172.00	$172.00
Purchase #5	$97.91	4.492%	$102.3081	$102.31	$102.30	$102.30
Purchase #6	$94.57	5.452%	$99.726	$99.73	$99.75	$99.70
Purchase #7	$61.84	8.497%	$67.0945	$67.09	$67.10	$67.10
7 purchase totals =	$760.18		$821.8687	$821.87	$821.85	$821.90