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	$93.69	3.874%	$97.3196	$97.32	$97.30	$97.30
Purchase #2	$47.71	3.166%	$49.2205	$49.22	$49.20	$49.20
Purchase #3	$248.70	12.298%	$279.2851	$279.29	$279.30	$279.30
Purchase #4	$200.40	11.531%	$223.5081	$223.51	$223.50	$223.50
Purchase #5	$136.81	10.145%	$150.6894	$150.69	$150.70	$150.70
Purchase #6	$142.53	7.520%	$153.2483	$153.25	$153.25	$153.20
Purchase #7	$159.29	3.152%	$164.3108	$164.31	$164.30	$164.30
7 purchase totals =	$1,029.13		$1,117.5818	$1,117.59	$1,117.55	$1,117.50