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	$180.80	11.111%	$200.8887	$200.89	$200.90	$200.90
Purchase #2	$165.66	10.411%	$182.9069	$182.91	$182.90	$182.90
Purchase #3	$60.32	11.361%	$67.173	$67.17	$67.15	$67.20
Purchase #4	$31.45	12.768%	$35.4655	$35.47	$35.45	$35.50
Purchase #5	$64.87	7.731%	$69.8851	$69.89	$69.90	$69.90
Purchase #6	$234.37	6.804%	$250.3165	$250.32	$250.30	$250.30
Purchase #7	$64.49	9.562%	$70.6565	$70.66	$70.65	$70.70
7 purchase totals =	$801.96		$877.2922	$877.31	$877.25	$877.40