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	$35.57	6.724%	$37.9617	$37.96	$37.95	$38.00
Purchase #2	$211.37	3.787%	$219.3746	$219.37	$219.35	$219.40
Purchase #3	$241.86	9.499%	$264.8343	$264.83	$264.85	$264.80
Purchase #4	$179.45	8.815%	$195.2685	$195.27	$195.25	$195.30
Purchase #5	$53.55	4.792%	$56.1161	$56.12	$56.10	$56.10
Purchase #6	$91.65	8.307%	$99.2634	$99.26	$99.25	$99.30
Purchase #7	$102.59	7.119%	$109.8934	$109.89	$109.90	$109.90
7 purchase totals =	$916.04		$982.7120	$982.70	$982.65	$982.80