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	$83.30	9.678%	$91.3618	$91.36	$91.35	$91.40
Purchase #2	$52.31	7.379%	$56.17	$56.17	$56.15	$56.20
Purchase #3	$114.49	7.779%	$123.3962	$123.40	$123.40	$123.40
Purchase #4	$218.33	13.731%	$248.3089	$248.31	$248.30	$248.30
Purchase #5	$240.52	13.807%	$273.7286	$273.73	$273.75	$273.70
Purchase #6	$92.27	8.457%	$100.0733	$100.07	$100.05	$100.10
Purchase #7	$70.27	11.466%	$78.3272	$78.33	$78.35	$78.30
7 purchase totals =	$871.49		$971.3660	$971.37	$971.35	$971.40