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	$208.32	12.765%	$234.912	$234.91	$234.90	$234.90
Purchase #2	$55.64	12.292%	$62.4793	$62.48	$62.50	$62.50
Purchase #3	$210.46	4.600%	$220.1412	$220.14	$220.15	$220.10
Purchase #4	$17.56	13.349%	$19.9041	$19.90	$19.90	$19.90
Purchase #5	$32.66	6.370%	$34.7404	$34.74	$34.75	$34.70
Purchase #6	$78.67	13.290%	$89.1252	$89.13	$89.15	$89.10
Purchase #7	$168.54	11.678%	$188.2221	$188.22	$188.20	$188.20
7 purchase totals =	$771.85		$849.5243	$849.52	$849.55	$849.40