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	$27.32	7.837%	$29.4611	$29.46	$29.45	$29.50
Purchase #2	$188.96	5.496%	$199.3452	$199.35	$199.35	$199.30
Purchase #3	$30.36	11.668%	$33.9024	$33.90	$33.90	$33.90
Purchase #4	$20.75	10.541%	$22.9373	$22.94	$22.95	$22.90
Purchase #5	$83.73	8.827%	$91.1208	$91.12	$91.10	$91.10
Purchase #6	$11.27	12.243%	$12.6498	$12.65	$12.65	$12.60
Purchase #7	$139.57	12.412%	$156.8934	$156.89	$156.90	$156.90
7 purchase totals =	$501.96		$546.3100	$546.31	$546.30	$546.20