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	$171.39	3.862%	$178.0091	$178.01	$178.00	$178.00
Purchase #2	$246.48	11.790%	$275.54	$275.54	$275.55	$275.50
Purchase #3	$13.89	10.199%	$15.3066	$15.31	$15.30	$15.30
Purchase #4	$35.74	4.852%	$37.4741	$37.47	$37.45	$37.50
Purchase #5	$74.96	11.190%	$83.348	$83.35	$83.35	$83.30
Purchase #6	$188.45	11.279%	$209.7053	$209.71	$209.70	$209.70
Purchase #7	$30.45	8.752%	$33.115	$33.12	$33.10	$33.10
7 purchase totals =	$761.36		$832.4981	$832.51	$832.45	$832.40