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	$123.88	10.705%	$137.1414	$137.14	$137.15	$137.10
Purchase #2	$17.86	13.746%	$20.315	$20.32	$20.30	$20.30
Purchase #3	$146.73	3.354%	$151.6513	$151.65	$151.65	$151.70
Purchase #4	$215.84	12.282%	$242.3495	$242.35	$242.35	$242.30
Purchase #5	$180.82	5.379%	$190.5463	$190.55	$190.55	$190.50
Purchase #6	$24.99	11.199%	$27.7886	$27.79	$27.80	$27.80
Purchase #7	$56.84	13.623%	$64.5833	$64.58	$64.60	$64.60
7 purchase totals =	$766.96		$834.3754	$834.38	$834.40	$834.30