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	$123.86	8.641%	$134.5627	$134.56	$134.55	$134.60
Purchase #2	$191.25	13.620%	$217.2983	$217.30	$217.30	$217.30
Purchase #3	$66.90	10.600%	$73.9914	$73.99	$74.00	$74.00
Purchase #4	$75.44	13.398%	$85.5475	$85.55	$85.55	$85.50
Purchase #5	$52.58	13.142%	$59.4901	$59.49	$59.50	$59.50
Purchase #6	$25.40	11.841%	$28.4076	$28.41	$28.40	$28.40
Purchase #7	$167.51	12.661%	$188.7184	$188.72	$188.70	$188.70
7 purchase totals =	$702.94		$788.0160	$788.02	$788.00	$788.00