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	$39.90	11.461%	$44.4729	$44.47	$44.45	$44.50
Purchase #2	$58.45	11.287%	$65.0473	$65.05	$65.05	$65.00
Purchase #3	$196.98	13.475%	$223.5231	$223.52	$223.50	$223.50
Purchase #4	$110.71	11.797%	$123.7705	$123.77	$123.75	$123.80
Purchase #5	$118.81	7.664%	$127.9156	$127.92	$127.90	$127.90
Purchase #6	$88.62	5.582%	$93.5668	$93.57	$93.55	$93.60
Purchase #7	$232.49	12.236%	$260.9375	$260.94	$260.95	$260.90
7 purchase totals =	$845.96		$939.2337	$939.24	$939.15	$939.20