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	$29.41	12.628%	$33.1239	$33.12	$33.10	$33.10
Purchase #2	$39.77	13.169%	$45.0073	$45.01	$45.00	$45.00
Purchase #3	$35.60	9.568%	$39.0062	$39.01	$39.00	$39.00
Purchase #4	$98.81	5.402%	$104.1477	$104.15	$104.15	$104.10
Purchase #5	$206.44	5.749%	$218.3082	$218.31	$218.30	$218.30
Purchase #6	$213.62	11.122%	$237.3788	$237.38	$237.40	$237.40
Purchase #7	$72.54	8.315%	$78.5717	$78.57	$78.55	$78.60
7 purchase totals =	$696.19		$755.5438	$755.55	$755.50	$755.50