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	$245.45	10.258%	$270.6283	$270.63	$270.65	$270.60
Purchase #2	$56.33	9.337%	$61.5895	$61.59	$61.60	$61.60
Purchase #3	$69.67	13.603%	$79.1472	$79.15	$79.15	$79.10
Purchase #4	$20.60	5.620%	$21.7577	$21.76	$21.75	$21.80
Purchase #5	$114.65	3.590%	$118.7659	$118.77	$118.75	$118.80
Purchase #6	$104.82	11.773%	$117.1605	$117.16	$117.15	$117.20
Purchase #7	$156.25	7.597%	$168.1203	$168.12	$168.10	$168.10
7 purchase totals =	$767.77		$837.1694	$837.18	$837.15	$837.20