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	$156.73	12.259%	$175.9435	$175.94	$175.95	$175.90
Purchase #2	$186.32	5.566%	$196.6906	$196.69	$196.70	$196.70
Purchase #3	$59.91	6.751%	$63.9545	$63.95	$63.95	$64.00
Purchase #4	$139.84	7.330%	$150.0903	$150.09	$150.10	$150.10
Purchase #5	$118.97	4.212%	$123.981	$123.98	$124.00	$124.00
Purchase #6	$89.58	12.809%	$101.0543	$101.05	$101.05	$101.10
Purchase #7	$91.48	9.475%	$100.1477	$100.15	$100.15	$100.10
7 purchase totals =	$842.83		$911.8619	$911.85	$911.90	$911.90