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	$20.33	6.363%	$21.6236	$21.62	$21.60	$21.60
Purchase #2	$219.44	13.267%	$248.5531	$248.55	$248.55	$248.60
Purchase #3	$6.84	7.697%	$7.3665	$7.37	$7.35	$7.40
Purchase #4	$164.56	6.717%	$175.6135	$175.61	$175.60	$175.60
Purchase #5	$229.27	10.137%	$252.5111	$252.51	$252.50	$252.50
Purchase #6	$82.32	11.590%	$91.8609	$91.86	$91.85	$91.90
Purchase #7	$135.56	12.779%	$152.8832	$152.88	$152.90	$152.90
7 purchase totals =	$858.32		$950.4119	$950.40	$950.35	$950.50