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	$7.50	5.423%	$7.9067	$7.91	$7.90	$7.90
Purchase #2	$19.46	3.573%	$20.1553	$20.16	$20.15	$20.20
Purchase #3	$160.56	11.532%	$179.0758	$179.08	$179.10	$179.10
Purchase #4	$84.56	5.708%	$89.3867	$89.39	$89.40	$89.40
Purchase #5	$97.95	11.186%	$108.9067	$108.91	$108.90	$108.90
Purchase #6	$109.89	12.124%	$123.2131	$123.21	$123.20	$123.20
Purchase #7	$168.37	3.193%	$173.7461	$173.75	$173.75	$173.70
7 purchase totals =	$648.29		$702.3904	$702.41	$702.40	$702.40