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	$37.98	3.366%	$39.2584	$39.26	$39.25	$39.30
Purchase #2	$243.91	12.710%	$274.911	$274.91	$274.90	$274.90
Purchase #3	$5.71	13.270%	$6.4677	$6.47	$6.45	$6.50
Purchase #4	$165.30	12.839%	$186.5229	$186.52	$186.50	$186.50
Purchase #5	$242.26	13.317%	$274.5218	$274.52	$274.50	$274.50
Purchase #6	$146.44	12.707%	$165.0481	$165.05	$165.05	$165.00
Purchase #7	$101.25	3.175%	$104.4647	$104.46	$104.45	$104.50
7 purchase totals =	$942.85		$1,051.1946	$1,051.19	$1,051.10	$1,051.20