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	$93.40	7.409%	$100.32	$100.32	$100.30	$100.30
Purchase #2	$47.39	6.123%	$50.2917	$50.29	$50.30	$50.30
Purchase #3	$221.38	6.814%	$236.4648	$236.46	$236.45	$236.50
Purchase #4	$120.93	8.413%	$131.1038	$131.10	$131.10	$131.10
Purchase #5	$109.30	6.400%	$116.2952	$116.30	$116.30	$116.30
Purchase #6	$31.28	9.675%	$34.3063	$34.31	$34.30	$34.30
Purchase #7	$21.86	11.781%	$24.4353	$24.44	$24.45	$24.40
7 purchase totals =	$645.54		$693.2171	$693.22	$693.20	$693.20