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	$250.76	12.801%	$282.8598	$282.86	$282.85	$282.90
Purchase #2	$152.62	11.765%	$170.5757	$170.58	$170.60	$170.60
Purchase #3	$236.93	11.429%	$264.0087	$264.01	$264.00	$264.00
Purchase #4	$45.42	10.625%	$50.2459	$50.25	$50.25	$50.20
Purchase #5	$93.39	7.847%	$100.7183	$100.72	$100.70	$100.70
Purchase #6	$25.41	13.558%	$28.8551	$28.86	$28.85	$28.90
Purchase #7	$186.63	6.144%	$198.0965	$198.10	$198.10	$198.10
7 purchase totals =	$991.16		$1,095.3600	$1,095.38	$1,095.35	$1,095.40