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	$36.26	10.149%	$39.94	$39.94	$39.95	$39.90
Purchase #2	$99.34	13.847%	$113.0956	$113.10	$113.10	$113.10
Purchase #3	$68.88	6.384%	$73.2773	$73.28	$73.30	$73.30
Purchase #4	$106.62	13.284%	$120.7834	$120.78	$120.80	$120.80
Purchase #5	$204.59	4.362%	$213.5142	$213.51	$213.50	$213.50
Purchase #6	$196.76	7.393%	$211.3065	$211.31	$211.30	$211.30
Purchase #7	$236.33	3.677%	$245.0199	$245.02	$245.00	$245.00
7 purchase totals =	$948.78		$1,016.9369	$1,016.94	$1,016.95	$1,016.90