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	$73.88	5.343%	$77.8274	$77.83	$77.85	$77.80
Purchase #2	$134.54	12.186%	$150.935	$150.94	$150.95	$150.90
Purchase #3	$126.48	12.525%	$142.3216	$142.32	$142.30	$142.30
Purchase #4	$203.83	7.245%	$218.5975	$218.60	$218.60	$218.60
Purchase #5	$123.64	3.765%	$128.295	$128.30	$128.30	$128.30
Purchase #6	$202.84	7.167%	$217.3775	$217.38	$217.40	$217.40
Purchase #7	$139.35	11.772%	$155.7543	$155.75	$155.75	$155.80
7 purchase totals =	$1,004.56		$1,091.1083	$1,091.12	$1,091.15	$1,091.10