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	$48.91	8.454%	$53.0449	$53.04	$53.05	$53.00
Purchase #2	$82.56	10.600%	$91.3114	$91.31	$91.30	$91.30
Purchase #3	$167.93	6.582%	$178.9832	$178.98	$179.00	$179.00
Purchase #4	$59.50	4.527%	$62.1936	$62.19	$62.20	$62.20
Purchase #5	$147.62	11.312%	$164.3188	$164.32	$164.30	$164.30
Purchase #6	$188.69	11.572%	$210.5252	$210.53	$210.55	$210.50
Purchase #7	$39.26	9.349%	$42.9304	$42.93	$42.95	$42.90
7 purchase totals =	$734.47		$803.3075	$803.30	$803.35	$803.20