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	$56.64	4.712%	$59.3089	$59.31	$59.30	$59.30
Purchase #2	$85.48	5.426%	$90.1181	$90.12	$90.10	$90.10
Purchase #3	$79.28	11.393%	$88.3124	$88.31	$88.30	$88.30
Purchase #4	$128.84	5.302%	$135.6711	$135.67	$135.65	$135.70
Purchase #5	$229.51	11.737%	$256.4476	$256.45	$256.45	$256.40
Purchase #6	$217.29	4.836%	$227.7981	$227.80	$227.80	$227.80
Purchase #7	$169.38	13.786%	$192.7307	$192.73	$192.75	$192.70
7 purchase totals =	$966.42		$1,050.3869	$1,050.39	$1,050.35	$1,050.30