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	$66.69	13.827%	$75.9112	$75.91	$75.90	$75.90
Purchase #2	$19.82	5.257%	$20.8619	$20.86	$20.85	$20.90
Purchase #3	$66.49	8.315%	$72.0186	$72.02	$72.00	$72.00
Purchase #4	$122.54	7.198%	$131.3604	$131.36	$131.35	$131.40
Purchase #5	$240.95	11.651%	$269.0231	$269.02	$269.00	$269.00
Purchase #6	$150.98	13.694%	$171.6552	$171.66	$171.65	$171.70
Purchase #7	$172.54	13.615%	$196.0313	$196.03	$196.05	$196.00
7 purchase totals =	$840.01		$936.8617	$936.86	$936.80	$936.90