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	$209.89	5.207%	$220.819	$220.82	$220.80	$220.80
Purchase #2	$139.44	12.492%	$156.8588	$156.86	$156.85	$156.90
Purchase #3	$13.50	13.444%	$15.3149	$15.31	$15.30	$15.30
Purchase #4	$149.38	10.778%	$165.4802	$165.48	$165.50	$165.50
Purchase #5	$136.56	13.200%	$154.5859	$154.59	$154.60	$154.60
Purchase #6	$13.45	4.220%	$14.0176	$14.02	$14.00	$14.00
Purchase #7	$250.53	7.521%	$269.3724	$269.37	$269.35	$269.40
7 purchase totals =	$912.75		$996.4488	$996.45	$996.40	$996.50