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	$134.90	9.196%	$147.3054	$147.31	$147.30	$147.30
Purchase #2	$180.44	5.545%	$190.4454	$190.45	$190.45	$190.40
Purchase #3	$32.69	12.725%	$36.8498	$36.85	$36.85	$36.80
Purchase #4	$57.89	3.460%	$59.893	$59.89	$59.90	$59.90
Purchase #5	$6.64	6.578%	$7.0768	$7.08	$7.10	$7.10
Purchase #6	$232.80	13.376%	$263.9393	$263.94	$263.95	$263.90
Purchase #7	$175.92	12.820%	$198.4729	$198.47	$198.45	$198.50
7 purchase totals =	$821.28		$903.9826	$903.99	$904.00	$903.90