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	$165.60	12.697%	$186.6262	$186.63	$186.65	$186.60
Purchase #2	$240.65	13.545%	$273.246	$273.25	$273.25	$273.20
Purchase #3	$109.89	4.459%	$114.79	$114.79	$114.80	$114.80
Purchase #4	$199.85	5.263%	$210.3681	$210.37	$210.35	$210.40
Purchase #5	$80.86	11.550%	$90.1993	$90.20	$90.20	$90.20
Purchase #6	$46.74	13.637%	$53.1139	$53.11	$53.10	$53.10
Purchase #7	$211.73	5.437%	$223.2418	$223.24	$223.25	$223.20
7 purchase totals =	$1,055.32		$1,151.5853	$1,151.59	$1,151.60	$1,151.50