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	$245.80	12.175%	$275.7262	$275.73	$275.75	$275.70
Purchase #2	$145.81	13.764%	$165.8793	$165.88	$165.90	$165.90
Purchase #3	$42.27	8.287%	$45.7729	$45.77	$45.75	$45.80
Purchase #4	$31.30	8.147%	$33.85	$33.85	$33.85	$33.90
Purchase #5	$71.43	12.857%	$80.6138	$80.61	$80.60	$80.60
Purchase #6	$218.58	12.246%	$245.3473	$245.35	$245.35	$245.30
Purchase #7	$150.76	3.352%	$155.8135	$155.81	$155.80	$155.80
7 purchase totals =	$905.95		$1,003.0030	$1,003.00	$1,003.00	$1,003.00