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	$70.84	10.166%	$78.0416	$78.04	$78.05	$78.00
Purchase #2	$75.61	8.501%	$82.0376	$82.04	$82.05	$82.00
Purchase #3	$172.45	10.660%	$190.8332	$190.83	$190.85	$190.80
Purchase #4	$34.35	11.591%	$38.3315	$38.33	$38.35	$38.30
Purchase #5	$97.62	13.447%	$110.747	$110.75	$110.75	$110.70
Purchase #6	$189.56	10.257%	$209.0032	$209.00	$209.00	$209.00
Purchase #7	$35.79	4.346%	$37.3454	$37.35	$37.35	$37.30
7 purchase totals =	$676.22		$746.3395	$746.34	$746.40	$746.10