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	$88.25	12.364%	$99.1612	$99.16	$99.15	$99.20
Purchase #2	$124.71	10.241%	$137.4816	$137.48	$137.50	$137.50
Purchase #3	$202.28	8.738%	$219.9552	$219.96	$219.95	$220.00
Purchase #4	$139.94	9.795%	$153.6471	$153.65	$153.65	$153.60
Purchase #5	$176.63	6.143%	$187.4804	$187.48	$187.50	$187.50
Purchase #6	$53.70	10.653%	$59.4207	$59.42	$59.40	$59.40
Purchase #7	$72.44	11.108%	$80.4866	$80.49	$80.50	$80.50
7 purchase totals =	$857.95		$937.6328	$937.64	$937.65	$937.70