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	$71.62	8.801%	$77.9233	$77.92	$77.90	$77.90
Purchase #2	$83.67	7.664%	$90.0825	$90.08	$90.10	$90.10
Purchase #3	$234.56	4.537%	$245.202	$245.20	$245.20	$245.20
Purchase #4	$95.27	4.560%	$99.6143	$99.61	$99.60	$99.60
Purchase #5	$218.52	11.813%	$244.3338	$244.33	$244.35	$244.30
Purchase #6	$166.66	10.102%	$183.496	$183.50	$183.50	$183.50
Purchase #7	$95.81	6.657%	$102.1881	$102.19	$102.20	$102.20
7 purchase totals =	$966.11		$1,042.8400	$1,042.83	$1,042.85	$1,042.80