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	$9.40	6.209%	$9.9836	$9.98	$10.00	$10.00
Purchase #2	$55.93	9.441%	$61.2104	$61.21	$61.20	$61.20
Purchase #3	$41.73	8.525%	$45.2875	$45.29	$45.30	$45.30
Purchase #4	$165.84	3.466%	$171.588	$171.59	$171.60	$171.60
Purchase #5	$249.54	4.505%	$260.7818	$260.78	$260.80	$260.80
Purchase #6	$33.81	5.765%	$35.7591	$35.76	$35.75	$35.80
Purchase #7	$178.86	9.653%	$196.1254	$196.13	$196.15	$196.10
7 purchase totals =	$735.11		$780.7358	$780.74	$780.80	$780.80