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	$77.98	9.471%	$85.3655	$85.37	$85.35	$85.40
Purchase #2	$161.56	12.829%	$182.2865	$182.29	$182.30	$182.30
Purchase #3	$158.72	13.694%	$180.4551	$180.46	$180.45	$180.50
Purchase #4	$31.95	10.539%	$35.3172	$35.32	$35.30	$35.30
Purchase #5	$245.56	3.842%	$254.9944	$254.99	$255.00	$255.00
Purchase #6	$27.87	3.671%	$28.8931	$28.89	$28.90	$28.90
Purchase #7	$69.40	13.290%	$78.6233	$78.62	$78.60	$78.60
7 purchase totals =	$773.04		$845.9351	$845.94	$845.90	$846.00