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	$129.31	10.489%	$142.8733	$142.87	$142.85	$142.90
Purchase #2	$82.33	12.855%	$92.9135	$92.91	$92.90	$92.90
Purchase #3	$238.97	7.321%	$256.465	$256.47	$256.45	$256.50
Purchase #4	$21.49	4.340%	$22.4227	$22.42	$22.40	$22.40
Purchase #5	$24.50	7.402%	$26.3135	$26.31	$26.30	$26.30
Purchase #6	$123.88	11.298%	$137.876	$137.88	$137.90	$137.90
Purchase #7	$148.46	5.533%	$156.6743	$156.67	$156.65	$156.70
7 purchase totals =	$768.94		$835.5383	$835.53	$835.45	$835.60