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	$101.51	11.655%	$113.341	$113.34	$113.35	$113.30
Purchase #2	$59.34	3.721%	$61.548	$61.55	$61.55	$61.50
Purchase #3	$90.43	9.826%	$99.3157	$99.32	$99.30	$99.30
Purchase #4	$134.75	12.539%	$151.6463	$151.65	$151.65	$151.60
Purchase #5	$191.88	10.611%	$212.2404	$212.24	$212.25	$212.20
Purchase #6	$79.46	8.709%	$86.3802	$86.38	$86.40	$86.40
Purchase #7	$178.96	8.540%	$194.2432	$194.24	$194.25	$194.20
7 purchase totals =	$836.33		$918.7148	$918.72	$918.75	$918.50