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	$27.30	4.824%	$28.617	$28.62	$28.60	$28.60
Purchase #2	$171.34	10.247%	$188.8972	$188.90	$188.90	$188.90
Purchase #3	$66.74	5.312%	$70.2852	$70.29	$70.30	$70.30
Purchase #4	$225.74	4.681%	$236.3069	$236.31	$236.30	$236.30
Purchase #5	$101.95	4.844%	$106.8885	$106.89	$106.90	$106.90
Purchase #6	$55.80	6.682%	$59.5286	$59.53	$59.55	$59.50
Purchase #7	$64.37	9.245%	$70.321	$70.32	$70.30	$70.30
7 purchase totals =	$713.24		$760.8444	$760.86	$760.85	$760.80