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	$33.76	11.234%	$37.5526	$37.55	$37.55	$37.60
Purchase #2	$50.25	7.721%	$54.1298	$54.13	$54.15	$54.10
Purchase #3	$212.28	13.308%	$240.5302	$240.53	$240.55	$240.50
Purchase #4	$18.63	13.651%	$21.1732	$21.17	$21.15	$21.20
Purchase #5	$94.35	13.856%	$107.4231	$107.42	$107.40	$107.40
Purchase #6	$165.35	8.614%	$179.5932	$179.59	$179.60	$179.60
Purchase #7	$210.83	13.365%	$239.0074	$239.01	$239.00	$239.00
7 purchase totals =	$785.45		$879.4095	$879.40	$879.40	$879.40