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	$38.47	9.446%	$42.1039	$42.10	$42.10	$42.10
Purchase #2	$149.83	8.638%	$162.7723	$162.77	$162.75	$162.80
Purchase #3	$214.84	11.510%	$239.5681	$239.57	$239.55	$239.60
Purchase #4	$100.53	4.389%	$104.9423	$104.94	$104.95	$104.90
Purchase #5	$159.56	9.340%	$174.4629	$174.46	$174.45	$174.50
Purchase #6	$182.79	3.244%	$188.7197	$188.72	$188.70	$188.70
Purchase #7	$165.80	3.607%	$171.7804	$171.78	$171.80	$171.80
7 purchase totals =	$1,011.82		$1,084.3496	$1,084.34	$1,084.30	$1,084.40