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	$75.30	7.482%	$80.9339	$80.93	$80.95	$80.90
Purchase #2	$46.63	13.760%	$53.0463	$53.05	$53.05	$53.00
Purchase #3	$138.48	9.846%	$152.1147	$152.11	$152.10	$152.10
Purchase #4	$167.34	4.165%	$174.3097	$174.31	$174.30	$174.30
Purchase #5	$70.50	10.681%	$78.0301	$78.03	$78.05	$78.00
Purchase #6	$160.45	13.174%	$181.5877	$181.59	$181.60	$181.60
Purchase #7	$188.55	11.431%	$210.1032	$210.10	$210.10	$210.10
7 purchase totals =	$847.25		$930.1256	$930.12	$930.15	$930.00