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	$132.65	6.654%	$141.4765	$141.48	$141.50	$141.50
Purchase #2	$30.92	13.724%	$35.1635	$35.16	$35.15	$35.20
Purchase #3	$54.73	11.302%	$60.9156	$60.92	$60.90	$60.90
Purchase #4	$37.82	11.135%	$42.0313	$42.03	$42.05	$42.00
Purchase #5	$62.79	13.188%	$71.0707	$71.07	$71.05	$71.10
Purchase #6	$79.96	8.694%	$86.9117	$86.91	$86.90	$86.90
Purchase #7	$182.89	11.275%	$203.5108	$203.51	$203.50	$203.50
7 purchase totals =	$581.76		$641.0801	$641.08	$641.05	$641.10