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	$181.48	9.724%	$199.1271	$199.13	$199.15	$199.10
Purchase #2	$160.30	9.681%	$175.8186	$175.82	$175.80	$175.80
Purchase #3	$119.81	6.759%	$127.908	$127.91	$127.90	$127.90
Purchase #4	$29.40	6.132%	$31.2028	$31.20	$31.20	$31.20
Purchase #5	$139.74	4.735%	$146.3567	$146.36	$146.35	$146.40
Purchase #6	$159.31	12.564%	$179.3257	$179.33	$179.35	$179.30
Purchase #7	$19.36	5.821%	$20.4869	$20.49	$20.50	$20.50
7 purchase totals =	$809.40		$880.2258	$880.24	$880.25	$880.20