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	$178.46	12.522%	$200.8068	$200.81	$200.80	$200.80
Purchase #2	$246.64	11.219%	$274.3105	$274.31	$274.30	$274.30
Purchase #3	$164.50	10.228%	$181.3251	$181.33	$181.35	$181.30
Purchase #4	$166.48	11.263%	$185.2306	$185.23	$185.25	$185.20
Purchase #5	$230.55	8.850%	$250.9537	$250.95	$250.95	$251.00
Purchase #6	$98.48	5.702%	$104.0953	$104.10	$104.10	$104.10
Purchase #7	$241.32	7.150%	$258.5744	$258.57	$258.55	$258.60
7 purchase totals =	$1,326.43		$1,455.2964	$1,455.30	$1,455.30	$1,455.30