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	$89.87	11.137%	$99.8788	$99.88	$99.90	$99.90
Purchase #2	$240.32	10.586%	$265.7603	$265.76	$265.75	$265.80
Purchase #3	$243.72	10.728%	$269.8663	$269.87	$269.85	$269.90
Purchase #4	$164.88	4.774%	$172.7514	$172.75	$172.75	$172.80
Purchase #5	$102.99	9.530%	$112.8049	$112.80	$112.80	$112.80
Purchase #6	$28.55	3.785%	$29.6306	$29.63	$29.65	$29.60
Purchase #7	$66.54	6.529%	$70.8844	$70.88	$70.90	$70.90
7 purchase totals =	$936.87		$1,021.5767	$1,021.57	$1,021.60	$1,021.70