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	$89.71	9.839%	$98.5366	$98.54	$98.55	$98.50
Purchase #2	$225.89	5.708%	$238.7838	$238.78	$238.80	$238.80
Purchase #3	$18.58	10.819%	$20.5902	$20.59	$20.60	$20.60
Purchase #4	$158.81	11.664%	$177.3336	$177.33	$177.35	$177.30
Purchase #5	$111.29	7.846%	$120.0218	$120.02	$120.00	$120.00
Purchase #6	$195.63	7.711%	$210.715	$210.72	$210.70	$210.70
Purchase #7	$137.85	6.499%	$146.8089	$146.81	$146.80	$146.80
7 purchase totals =	$937.76		$1,012.7899	$1,012.79	$1,012.80	$1,012.70