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	$171.30	9.442%	$187.4741	$187.47	$187.45	$187.50
Purchase #2	$122.40	11.634%	$136.64	$136.64	$136.65	$136.60
Purchase #3	$232.83	11.148%	$258.7859	$258.79	$258.80	$258.80
Purchase #4	$71.40	3.466%	$73.8747	$73.87	$73.85	$73.90
Purchase #5	$152.75	11.829%	$170.8188	$170.82	$170.80	$170.80
Purchase #6	$59.42	13.293%	$67.3187	$67.32	$67.30	$67.30
Purchase #7	$80.93	3.268%	$83.5748	$83.57	$83.55	$83.60
7 purchase totals =	$891.03		$978.4870	$978.48	$978.40	$978.50