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	$53.35	10.576%	$58.9923	$58.99	$59.00	$59.00
Purchase #2	$233.88	6.751%	$249.6692	$249.67	$249.65	$249.70
Purchase #3	$99.25	3.820%	$103.0414	$103.04	$103.05	$103.00
Purchase #4	$79.92	11.850%	$89.3905	$89.39	$89.40	$89.40
Purchase #5	$41.61	5.826%	$44.0342	$44.03	$44.05	$44.00
Purchase #6	$115.73	13.772%	$131.6683	$131.67	$131.65	$131.70
Purchase #7	$149.79	10.515%	$165.5404	$165.54	$165.55	$165.50
7 purchase totals =	$773.53		$842.3363	$842.33	$842.35	$842.30