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	$61.82	4.405%	$64.5432	$64.54	$64.55	$64.50
Purchase #2	$54.47	3.780%	$56.529	$56.53	$56.55	$56.50
Purchase #3	$13.95	10.383%	$15.3984	$15.40	$15.40	$15.40
Purchase #4	$110.57	4.392%	$115.4262	$115.43	$115.45	$115.40
Purchase #5	$227.69	10.204%	$250.9235	$250.92	$250.90	$250.90
Purchase #6	$40.50	4.332%	$42.2545	$42.25	$42.25	$42.30
Purchase #7	$82.65	7.276%	$88.6636	$88.66	$88.65	$88.70
7 purchase totals =	$591.65		$633.7384	$633.73	$633.75	$633.70