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	$123.57	6.584%	$131.7058	$131.71	$131.70	$131.70
Purchase #2	$7.63	11.580%	$8.5136	$8.51	$8.50	$8.50
Purchase #3	$243.75	9.207%	$266.1921	$266.19	$266.20	$266.20
Purchase #4	$187.70	6.636%	$200.1558	$200.16	$200.15	$200.20
Purchase #5	$166.59	4.685%	$174.3947	$174.39	$174.40	$174.40
Purchase #6	$186.36	12.554%	$209.7556	$209.76	$209.75	$209.80
Purchase #7	$89.60	12.368%	$100.6817	$100.68	$100.70	$100.70
7 purchase totals =	$1,005.20		$1,091.3993	$1,091.40	$1,091.40	$1,091.50