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	$27.33	9.140%	$29.828	$29.83	$29.85	$29.80
Purchase #2	$194.56	12.726%	$219.3197	$219.32	$219.30	$219.30
Purchase #3	$107.92	7.350%	$115.8521	$115.85	$115.85	$115.90
Purchase #4	$90.34	11.385%	$100.6252	$100.63	$100.65	$100.60
Purchase #5	$80.96	11.870%	$90.57	$90.57	$90.55	$90.60
Purchase #6	$81.26	3.224%	$83.8798	$83.88	$83.90	$83.90
Purchase #7	$58.33	8.340%	$63.1947	$63.19	$63.20	$63.20
7 purchase totals =	$640.70		$703.2695	$703.27	$703.30	$703.30