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	$52.39	12.809%	$59.1006	$59.10	$59.10	$59.10
Purchase #2	$57.92	7.575%	$62.3074	$62.31	$62.30	$62.30
Purchase #3	$235.49	5.513%	$248.4726	$248.47	$248.45	$248.50
Purchase #4	$56.46	7.387%	$60.6307	$60.63	$60.65	$60.60
Purchase #5	$89.89	5.533%	$94.8636	$94.86	$94.85	$94.90
Purchase #6	$196.77	9.424%	$215.3136	$215.31	$215.30	$215.30
Purchase #7	$90.29	13.804%	$102.7536	$102.75	$102.75	$102.80
7 purchase totals =	$779.21		$843.4421	$843.43	$843.40	$843.50