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	$94.98	4.386%	$99.1458	$99.15	$99.15	$99.10
Purchase #2	$232.82	10.623%	$257.5525	$257.55	$257.55	$257.60
Purchase #3	$130.43	6.728%	$139.2053	$139.21	$139.20	$139.20
Purchase #4	$53.84	10.513%	$59.5002	$59.50	$59.50	$59.50
Purchase #5	$131.51	10.510%	$145.3317	$145.33	$145.35	$145.30
Purchase #6	$55.96	4.393%	$58.4183	$58.42	$58.40	$58.40
Purchase #7	$231.58	6.212%	$245.9657	$245.97	$245.95	$246.00
7 purchase totals =	$931.12		$1,005.1195	$1,005.13	$1,005.10	$1,005.10