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	$124.37	13.600%	$141.2843	$141.28	$141.30	$141.30
Purchase #2	$63.75	4.411%	$66.562	$66.56	$66.55	$66.60
Purchase #3	$200.80	4.454%	$209.7436	$209.74	$209.75	$209.70
Purchase #4	$154.52	8.412%	$167.5182	$167.52	$167.50	$167.50
Purchase #5	$131.88	12.556%	$148.4389	$148.44	$148.45	$148.40
Purchase #6	$187.26	12.586%	$210.8285	$210.83	$210.85	$210.80
Purchase #7	$27.96	3.189%	$28.8516	$28.85	$28.85	$28.90
7 purchase totals =	$890.54		$973.2271	$973.22	$973.25	$973.20