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	$234.45	4.181%	$244.2524	$244.25	$244.25	$244.30
Purchase #2	$29.29	7.697%	$31.5445	$31.54	$31.55	$31.50
Purchase #3	$177.42	10.743%	$196.4802	$196.48	$196.50	$196.50
Purchase #4	$239.87	12.385%	$269.5779	$269.58	$269.60	$269.60
Purchase #5	$188.60	8.359%	$204.3651	$204.37	$204.35	$204.40
Purchase #6	$186.39	10.686%	$206.3076	$206.31	$206.30	$206.30
Purchase #7	$35.74	9.827%	$39.2522	$39.25	$39.25	$39.30
7 purchase totals =	$1,091.76		$1,191.7799	$1,191.78	$1,191.80	$1,191.90