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	$56.61	13.397%	$64.194	$64.19	$64.20	$64.20
Purchase #2	$37.87	6.687%	$40.4024	$40.40	$40.40	$40.40
Purchase #3	$142.94	13.668%	$162.477	$162.48	$162.50	$162.50
Purchase #4	$155.30	6.764%	$165.8045	$165.80	$165.80	$165.80
Purchase #5	$35.25	9.814%	$38.7094	$38.71	$38.70	$38.70
Purchase #6	$119.65	6.483%	$127.4069	$127.41	$127.40	$127.40
Purchase #7	$237.42	13.818%	$270.2267	$270.23	$270.25	$270.20
7 purchase totals =	$785.04		$869.2209	$869.22	$869.25	$869.20