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	$148.95	5.834%	$157.6397	$157.64	$157.65	$157.60
Purchase #2	$94.40	11.579%	$105.3306	$105.33	$105.35	$105.30
Purchase #3	$52.54	7.612%	$56.5393	$56.54	$56.55	$56.50
Purchase #4	$52.34	5.390%	$55.1611	$55.16	$55.15	$55.20
Purchase #5	$123.92	12.503%	$139.4137	$139.41	$139.40	$139.40
Purchase #6	$7.88	13.129%	$8.9146	$8.91	$8.90	$8.90
Purchase #7	$40.56	7.340%	$43.5371	$43.54	$43.55	$43.50
7 purchase totals =	$520.59		$566.5361	$566.53	$566.55	$566.40