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	$240.25	10.420%	$265.2841	$265.28	$265.30	$265.30
Purchase #2	$220.93	10.337%	$243.7675	$243.77	$243.75	$243.80
Purchase #3	$120.98	5.226%	$127.3024	$127.30	$127.30	$127.30
Purchase #4	$124.96	13.449%	$141.7659	$141.77	$141.75	$141.80
Purchase #5	$54.77	9.813%	$60.1446	$60.14	$60.15	$60.10
Purchase #6	$103.71	5.741%	$109.664	$109.66	$109.65	$109.70
Purchase #7	$84.57	7.440%	$90.862	$90.86	$90.85	$90.90
7 purchase totals =	$950.17		$1,038.7905	$1,038.78	$1,038.75	$1,038.90