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	$25.48	6.498%	$27.1357	$27.14	$27.15	$27.10
Purchase #2	$127.70	11.262%	$142.0816	$142.08	$142.10	$142.10
Purchase #3	$168.70	10.765%	$186.8606	$186.86	$186.85	$186.90
Purchase #4	$46.62	4.513%	$48.724	$48.72	$48.70	$48.70
Purchase #5	$148.92	10.486%	$164.5358	$164.54	$164.55	$164.50
Purchase #6	$244.36	9.166%	$266.758	$266.76	$266.75	$266.80
Purchase #7	$221.46	10.574%	$244.8772	$244.88	$244.90	$244.90
7 purchase totals =	$983.24		$1,080.9729	$1,080.98	$1,081.00	$1,081.00