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	$62.39	8.289%	$67.5615	$67.56	$67.55	$67.60
Purchase #2	$67.89	3.274%	$70.1127	$70.11	$70.10	$70.10
Purchase #3	$47.50	9.614%	$52.0667	$52.07	$52.05	$52.10
Purchase #4	$204.84	5.719%	$216.5548	$216.55	$216.55	$216.60
Purchase #5	$126.83	12.663%	$142.8905	$142.89	$142.90	$142.90
Purchase #6	$113.93	9.505%	$124.759	$124.76	$124.75	$124.80
Purchase #7	$94.90	4.461%	$99.1335	$99.13	$99.15	$99.10
7 purchase totals =	$718.28		$773.0787	$773.07	$773.05	$773.20