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	$160.98	11.256%	$179.0999	$179.10	$179.10	$179.10
Purchase #2	$35.77	5.476%	$37.7288	$37.73	$37.75	$37.70
Purchase #3	$164.67	3.171%	$169.8917	$169.89	$169.90	$169.90
Purchase #4	$203.28	11.428%	$226.5108	$226.51	$226.50	$226.50
Purchase #5	$172.68	5.811%	$182.7144	$182.71	$182.70	$182.70
Purchase #6	$145.48	9.635%	$159.497	$159.50	$159.50	$159.50
Purchase #7	$40.55	4.760%	$42.4802	$42.48	$42.50	$42.50
7 purchase totals =	$923.41		$997.9228	$997.92	$997.95	$997.90