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	$165.54	9.237%	$180.8309	$180.83	$180.85	$180.80
Purchase #2	$106.76	9.496%	$116.8979	$116.90	$116.90	$116.90
Purchase #3	$149.41	11.535%	$166.6444	$166.64	$166.65	$166.60
Purchase #4	$188.74	4.172%	$196.6142	$196.61	$196.60	$196.60
Purchase #5	$83.85	7.641%	$90.257	$90.26	$90.25	$90.30
Purchase #6	$187.86	12.592%	$211.5153	$211.52	$211.50	$211.50
Purchase #7	$82.84	6.368%	$88.1153	$88.12	$88.10	$88.10
7 purchase totals =	$965.00		$1,050.8750	$1,050.88	$1,050.85	$1,050.80