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	$7.83	5.538%	$8.2636	$8.26	$8.25	$8.30
Purchase #2	$63.49	11.558%	$70.8282	$70.83	$70.85	$70.80
Purchase #3	$173.50	3.161%	$178.9843	$178.98	$179.00	$179.00
Purchase #4	$206.91	7.373%	$222.1655	$222.17	$222.15	$222.20
Purchase #5	$59.67	3.730%	$61.8957	$61.90	$61.90	$61.90
Purchase #6	$243.45	11.139%	$270.5679	$270.57	$270.55	$270.60
Purchase #7	$220.70	13.465%	$250.4173	$250.42	$250.40	$250.40
7 purchase totals =	$975.55		$1,063.1225	$1,063.13	$1,063.10	$1,063.20