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	$51.43	8.800%	$55.9558	$55.96	$55.95	$56.00
Purchase #2	$82.71	9.596%	$90.6469	$90.65	$90.65	$90.60
Purchase #3	$36.28	10.623%	$40.134	$40.13	$40.15	$40.10
Purchase #4	$59.32	9.143%	$64.7436	$64.74	$64.75	$64.70
Purchase #5	$195.47	13.617%	$222.0871	$222.09	$222.10	$222.10
Purchase #6	$25.57	4.543%	$26.7316	$26.73	$26.75	$26.70
Purchase #7	$91.61	12.248%	$102.8304	$102.83	$102.85	$102.80
7 purchase totals =	$542.39		$603.1294	$603.13	$603.20	$603.00