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	$72.97	7.289%	$78.2888	$78.29	$78.30	$78.30
Purchase #2	$243.50	13.285%	$275.849	$275.85	$275.85	$275.80
Purchase #3	$243.60	7.770%	$262.5277	$262.53	$262.55	$262.50
Purchase #4	$156.71	11.104%	$174.1111	$174.11	$174.10	$174.10
Purchase #5	$85.44	5.577%	$90.205	$90.21	$90.20	$90.20
Purchase #6	$139.75	6.593%	$148.9637	$148.96	$148.95	$149.00
Purchase #7	$20.54	13.542%	$23.3215	$23.32	$23.30	$23.30
7 purchase totals =	$962.51		$1,053.2668	$1,053.27	$1,053.25	$1,053.20