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	$55.25	12.871%	$62.3612	$62.36	$62.35	$62.40
Purchase #2	$58.55	10.267%	$64.5613	$64.56	$64.55	$64.60
Purchase #3	$237.40	13.469%	$269.3754	$269.38	$269.40	$269.40
Purchase #4	$148.46	11.343%	$165.2998	$165.30	$165.30	$165.30
Purchase #5	$189.59	4.464%	$198.0533	$198.05	$198.05	$198.10
Purchase #6	$180.38	8.234%	$195.2325	$195.23	$195.25	$195.20
Purchase #7	$235.59	8.403%	$255.3866	$255.39	$255.40	$255.40
7 purchase totals =	$1,105.22		$1,210.2701	$1,210.27	$1,210.30	$1,210.40