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	$34.62	7.674%	$37.2767	$37.28	$37.30	$37.30
Purchase #2	$171.50	5.553%	$181.0234	$181.02	$181.00	$181.00
Purchase #3	$148.47	10.720%	$164.386	$164.39	$164.40	$164.40
Purchase #4	$11.38	8.304%	$12.325	$12.33	$12.35	$12.30
Purchase #5	$94.42	12.681%	$106.3934	$106.39	$106.40	$106.40
Purchase #6	$60.69	11.277%	$67.534	$67.53	$67.55	$67.50
Purchase #7	$76.37	6.112%	$81.0377	$81.04	$81.05	$81.00
7 purchase totals =	$597.45		$649.9762	$649.98	$650.05	$649.90