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	$125.66	8.430%	$136.2531	$136.25	$136.25	$136.30
Purchase #2	$84.36	6.384%	$89.7455	$89.75	$89.75	$89.70
Purchase #3	$129.61	11.862%	$144.9843	$144.98	$145.00	$145.00
Purchase #4	$229.85	5.818%	$243.2227	$243.22	$243.20	$243.20
Purchase #5	$91.69	10.474%	$101.2936	$101.29	$101.30	$101.30
Purchase #6	$112.94	12.547%	$127.1106	$127.11	$127.10	$127.10
Purchase #7	$223.68	11.451%	$249.2936	$249.29	$249.30	$249.30
7 purchase totals =	$997.79		$1,091.9034	$1,091.89	$1,091.90	$1,091.90