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	$50.80	4.334%	$53.0017	$53.00	$53.00	$53.00
Purchase #2	$84.96	6.276%	$90.2921	$90.29	$90.30	$90.30
Purchase #3	$226.57	8.476%	$245.7741	$245.77	$245.75	$245.80
Purchase #4	$180.88	9.238%	$197.5897	$197.59	$197.60	$197.60
Purchase #5	$212.33	8.218%	$229.7793	$229.78	$229.80	$229.80
Purchase #6	$236.41	8.110%	$255.5829	$255.58	$255.60	$255.60
Purchase #7	$52.34	7.221%	$56.1195	$56.12	$56.10	$56.10
7 purchase totals =	$1,044.29		$1,128.1393	$1,128.13	$1,128.15	$1,128.20