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	$204.98	8.523%	$222.4504	$222.45	$222.45	$222.50
Purchase #2	$234.62	6.773%	$250.5108	$250.51	$250.50	$250.50
Purchase #3	$70.48	11.712%	$78.7346	$78.73	$78.75	$78.70
Purchase #4	$159.93	11.300%	$178.0021	$178.00	$178.00	$178.00
Purchase #5	$88.27	3.360%	$91.2359	$91.24	$91.25	$91.20
Purchase #6	$81.57	3.638%	$84.5375	$84.54	$84.55	$84.50
Purchase #7	$88.40	4.555%	$92.4266	$92.43	$92.45	$92.40
7 purchase totals =	$928.25		$997.8979	$997.90	$997.95	$997.80