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	$90.89	12.813%	$102.5357	$102.54	$102.55	$102.50
Purchase #2	$156.80	9.225%	$171.2648	$171.26	$171.25	$171.30
Purchase #3	$99.42	11.395%	$110.7489	$110.75	$110.75	$110.70
Purchase #4	$164.91	11.736%	$184.2638	$184.26	$184.25	$184.30
Purchase #5	$208.70	3.289%	$215.5641	$215.56	$215.55	$215.60
Purchase #6	$61.88	6.403%	$65.8422	$65.84	$65.85	$65.80
Purchase #7	$196.86	8.874%	$214.3294	$214.33	$214.35	$214.30
7 purchase totals =	$979.46		$1,064.5489	$1,064.54	$1,064.55	$1,064.50