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	$80.41	12.167%	$90.1935	$90.19	$90.20	$90.20
Purchase #2	$109.95	3.819%	$114.149	$114.15	$114.15	$114.10
Purchase #3	$28.65	8.343%	$31.0403	$31.04	$31.05	$31.00
Purchase #4	$245.69	9.713%	$269.5539	$269.55	$269.55	$269.60
Purchase #5	$24.89	9.472%	$27.2476	$27.25	$27.25	$27.20
Purchase #6	$65.51	7.695%	$70.551	$70.55	$70.55	$70.60
Purchase #7	$226.78	9.723%	$248.8298	$248.83	$248.85	$248.80
7 purchase totals =	$781.88		$851.5651	$851.56	$851.60	$851.50