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	$156.89	13.424%	$177.9509	$177.95	$177.95	$178.00
Purchase #2	$142.33	3.121%	$146.7721	$146.77	$146.75	$146.80
Purchase #3	$33.94	13.289%	$38.4503	$38.45	$38.45	$38.50
Purchase #4	$239.33	6.315%	$254.4437	$254.44	$254.45	$254.40
Purchase #5	$96.59	10.661%	$106.8875	$106.89	$106.90	$106.90
Purchase #6	$110.87	12.282%	$124.4871	$124.49	$124.50	$124.50
Purchase #7	$49.50	9.557%	$54.2307	$54.23	$54.25	$54.20
7 purchase totals =	$829.45		$903.2223	$903.22	$903.25	$903.30