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	$164.66	8.519%	$178.6874	$178.69	$178.70	$178.70
Purchase #2	$38.61	8.317%	$41.8212	$41.82	$41.80	$41.80
Purchase #3	$96.90	7.162%	$103.84	$103.84	$103.85	$103.80
Purchase #4	$82.85	8.513%	$89.903	$89.90	$89.90	$89.90
Purchase #5	$19.58	3.167%	$20.2001	$20.20	$20.20	$20.20
Purchase #6	$123.62	13.339%	$140.1097	$140.11	$140.10	$140.10
Purchase #7	$89.98	7.657%	$96.8698	$96.87	$96.85	$96.90
7 purchase totals =	$616.20		$671.4312	$671.43	$671.40	$671.40