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	$172.61	10.834%	$191.3106	$191.31	$191.30	$191.30
Purchase #2	$157.65	5.232%	$165.8982	$165.90	$165.90	$165.90
Purchase #3	$69.53	4.544%	$72.6894	$72.69	$72.70	$72.70
Purchase #4	$233.59	13.380%	$264.8443	$264.84	$264.85	$264.80
Purchase #5	$114.88	11.363%	$127.9338	$127.93	$127.95	$127.90
Purchase #6	$58.54	6.576%	$62.3896	$62.39	$62.40	$62.40
Purchase #7	$82.96	10.646%	$91.7919	$91.79	$91.80	$91.80
7 purchase totals =	$889.76		$976.8578	$976.85	$976.90	$976.80