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	$43.72	7.503%	$47.0003	$47.00	$47.00	$47.00
Purchase #2	$54.94	9.460%	$60.1373	$60.14	$60.15	$60.10
Purchase #3	$235.48	12.288%	$264.4158	$264.42	$264.40	$264.40
Purchase #4	$127.69	11.589%	$142.488	$142.49	$142.50	$142.50
Purchase #5	$168.86	7.426%	$181.3995	$181.40	$181.40	$181.40
Purchase #6	$187.73	12.171%	$210.5786	$210.58	$210.60	$210.60
Purchase #7	$84.54	8.294%	$91.5517	$91.55	$91.55	$91.60
7 purchase totals =	$902.96		$997.5712	$997.58	$997.60	$997.60