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	$153.54	3.180%	$158.4226	$158.42	$158.40	$158.40
Purchase #2	$73.47	11.702%	$82.0675	$82.07	$82.05	$82.10
Purchase #3	$170.83	5.345%	$179.9609	$179.96	$179.95	$180.00
Purchase #4	$62.34	9.256%	$68.1102	$68.11	$68.10	$68.10
Purchase #5	$222.74	8.255%	$241.1272	$241.13	$241.15	$241.10
Purchase #6	$98.84	5.107%	$103.8878	$103.89	$103.90	$103.90
Purchase #7	$98.70	5.294%	$103.9252	$103.93	$103.95	$103.90
7 purchase totals =	$880.46		$937.5014	$937.51	$937.50	$937.50