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	$125.69	8.310%	$136.1348	$136.13	$136.15	$136.10
Purchase #2	$60.87	10.695%	$67.38	$67.38	$67.40	$67.40
Purchase #3	$171.36	4.771%	$179.5356	$179.54	$179.55	$179.50
Purchase #4	$143.92	4.613%	$150.559	$150.56	$150.55	$150.60
Purchase #5	$72.53	13.326%	$82.1953	$82.20	$82.20	$82.20
Purchase #6	$121.81	9.546%	$133.438	$133.44	$133.45	$133.40
Purchase #7	$91.88	11.271%	$102.2358	$102.24	$102.25	$102.20
7 purchase totals =	$788.06		$851.4785	$851.49	$851.55	$851.40