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	$91.95	11.486%	$102.5114	$102.51	$102.50	$102.50
Purchase #2	$210.61	6.222%	$223.7142	$223.71	$223.70	$223.70
Purchase #3	$48.36	12.398%	$54.3557	$54.36	$54.35	$54.40
Purchase #4	$64.96	11.322%	$72.3148	$72.31	$72.30	$72.30
Purchase #5	$174.69	3.259%	$180.3831	$180.38	$180.40	$180.40
Purchase #6	$239.28	10.393%	$264.1484	$264.15	$264.15	$264.10
Purchase #7	$86.28	10.683%	$95.4973	$95.50	$95.50	$95.50
7 purchase totals =	$916.13		$992.9249	$992.92	$992.90	$992.90