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	$102.90	6.227%	$109.3076	$109.31	$109.30	$109.30
Purchase #2	$102.78	6.735%	$109.7022	$109.70	$109.70	$109.70
Purchase #3	$188.58	13.383%	$213.8177	$213.82	$213.80	$213.80
Purchase #4	$140.91	9.407%	$154.1654	$154.17	$154.15	$154.20
Purchase #5	$240.51	3.687%	$249.3776	$249.38	$249.40	$249.40
Purchase #6	$230.79	4.257%	$240.6147	$240.61	$240.60	$240.60
Purchase #7	$85.86	4.321%	$89.57	$89.57	$89.55	$89.60
7 purchase totals =	$1,092.33		$1,166.5552	$1,166.56	$1,166.50	$1,166.60