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	$229.42	5.226%	$241.4095	$241.41	$241.40	$241.40
Purchase #2	$133.72	6.204%	$142.016	$142.02	$142.00	$142.00
Purchase #3	$23.59	7.303%	$25.3128	$25.31	$25.30	$25.30
Purchase #4	$136.82	11.345%	$152.3422	$152.34	$152.35	$152.30
Purchase #5	$147.88	7.168%	$158.48	$158.48	$158.50	$158.50
Purchase #6	$179.82	6.134%	$190.8502	$190.85	$190.85	$190.90
Purchase #7	$53.82	13.546%	$61.1105	$61.11	$61.10	$61.10
7 purchase totals =	$905.07		$971.5212	$971.52	$971.50	$971.50