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	$227.74	12.717%	$256.7017	$256.70	$256.70	$256.70
Purchase #2	$158.51	13.624%	$180.1054	$180.11	$180.10	$180.10
Purchase #3	$159.56	10.184%	$175.8096	$175.81	$175.80	$175.80
Purchase #4	$26.96	5.515%	$28.4468	$28.45	$28.45	$28.40
Purchase #5	$98.77	13.627%	$112.2294	$112.23	$112.25	$112.20
Purchase #6	$123.27	6.380%	$131.1346	$131.13	$131.15	$131.10
Purchase #7	$86.93	6.215%	$92.3327	$92.33	$92.35	$92.30
7 purchase totals =	$881.74		$976.7602	$976.76	$976.80	$976.60