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	$37.34	5.336%	$39.3325	$39.33	$39.35	$39.30
Purchase #2	$79.86	11.653%	$89.1661	$89.17	$89.15	$89.20
Purchase #3	$72.89	13.150%	$82.475	$82.48	$82.50	$82.50
Purchase #4	$124.35	8.627%	$135.0777	$135.08	$135.10	$135.10
Purchase #5	$40.88	12.383%	$45.9422	$45.94	$45.95	$45.90
Purchase #6	$185.84	13.404%	$210.75	$210.75	$210.75	$210.80
Purchase #7	$151.50	9.213%	$165.4577	$165.46	$165.45	$165.50
7 purchase totals =	$692.66		$768.2012	$768.21	$768.25	$768.30