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	$198.85	11.275%	$221.2703	$221.27	$221.25	$221.30
Purchase #2	$115.67	11.371%	$128.8228	$128.82	$128.80	$128.80
Purchase #3	$60.62	4.556%	$63.3818	$63.38	$63.40	$63.40
Purchase #4	$167.51	11.485%	$186.7485	$186.75	$186.75	$186.70
Purchase #5	$31.81	10.165%	$35.0435	$35.04	$35.05	$35.00
Purchase #6	$19.50	9.188%	$21.2917	$21.29	$21.30	$21.30
Purchase #7	$77.29	11.148%	$85.9063	$85.91	$85.90	$85.90
7 purchase totals =	$671.25		$742.4649	$742.46	$742.45	$742.40