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	$167.69	13.218%	$189.8553	$189.86	$189.85	$189.90
Purchase #2	$47.35	12.474%	$53.2564	$53.26	$53.25	$53.30
Purchase #3	$215.66	8.497%	$233.9846	$233.98	$234.00	$234.00
Purchase #4	$54.46	9.218%	$59.4801	$59.48	$59.50	$59.50
Purchase #5	$209.87	13.447%	$238.0912	$238.09	$238.10	$238.10
Purchase #6	$90.40	7.365%	$97.058	$97.06	$97.05	$97.10
Purchase #7	$102.83	12.307%	$115.4853	$115.49	$115.50	$115.50
7 purchase totals =	$888.26		$987.2109	$987.22	$987.25	$987.40