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	$250.28	3.669%	$259.4628	$259.46	$259.45	$259.50
Purchase #2	$82.30	4.342%	$85.8735	$85.87	$85.85	$85.90
Purchase #3	$76.48	9.424%	$83.6875	$83.69	$83.70	$83.70
Purchase #4	$96.88	7.496%	$104.1421	$104.14	$104.15	$104.10
Purchase #5	$53.89	8.131%	$58.2718	$58.27	$58.25	$58.30
Purchase #6	$77.85	13.392%	$88.2757	$88.28	$88.30	$88.30
Purchase #7	$98.98	10.285%	$109.1601	$109.16	$109.15	$109.20
7 purchase totals =	$736.66		$788.8735	$788.87	$788.85	$789.00