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	$177.71	5.791%	$188.0012	$188.00	$188.00	$188.00
Purchase #2	$130.73	9.410%	$143.0317	$143.03	$143.05	$143.00
Purchase #3	$30.54	4.131%	$31.8016	$31.80	$31.80	$31.80
Purchase #4	$12.32	5.200%	$12.9606	$12.96	$12.95	$13.00
Purchase #5	$19.29	11.583%	$21.5244	$21.52	$21.50	$21.50
Purchase #6	$194.36	11.377%	$216.4723	$216.47	$216.45	$216.50
Purchase #7	$53.33	4.134%	$55.5347	$55.53	$55.55	$55.50
7 purchase totals =	$618.28		$669.3265	$669.31	$669.30	$669.30