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	$210.60	5.374%	$221.9176	$221.92	$221.90	$221.90
Purchase #2	$133.67	13.798%	$152.1138	$152.11	$152.10	$152.10
Purchase #3	$71.48	3.444%	$73.9418	$73.94	$73.95	$73.90
Purchase #4	$171.72	5.172%	$180.6014	$180.60	$180.60	$180.60
Purchase #5	$85.35	5.687%	$90.2039	$90.20	$90.20	$90.20
Purchase #6	$205.25	10.756%	$227.3267	$227.33	$227.35	$227.30
Purchase #7	$135.46	6.423%	$144.1606	$144.16	$144.15	$144.20
7 purchase totals =	$1,013.53		$1,090.2658	$1,090.26	$1,090.25	$1,090.20