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	$178.85	5.606%	$188.8763	$188.88	$188.90	$188.90
Purchase #2	$93.80	8.501%	$101.7739	$101.77	$101.75	$101.80
Purchase #3	$57.69	13.682%	$65.5831	$65.58	$65.60	$65.60
Purchase #4	$71.45	8.504%	$77.5261	$77.53	$77.55	$77.50
Purchase #5	$43.86	3.654%	$45.4626	$45.46	$45.45	$45.50
Purchase #6	$170.48	12.589%	$191.9417	$191.94	$191.95	$191.90
Purchase #7	$135.97	11.835%	$152.062	$152.06	$152.05	$152.10
7 purchase totals =	$752.10		$823.2257	$823.22	$823.25	$823.30