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	$84.79	5.294%	$89.2788	$89.28	$89.30	$89.30
Purchase #2	$12.38	11.438%	$13.796	$13.80	$13.80	$13.80
Purchase #3	$23.56	4.639%	$24.6529	$24.65	$24.65	$24.70
Purchase #4	$131.60	3.718%	$136.4929	$136.49	$136.50	$136.50
Purchase #5	$72.80	6.752%	$77.7155	$77.72	$77.70	$77.70
Purchase #6	$168.99	12.718%	$190.4821	$190.48	$190.50	$190.50
Purchase #7	$65.36	9.759%	$71.7385	$71.74	$71.75	$71.70
7 purchase totals =	$559.48		$604.1567	$604.16	$604.20	$604.20