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	$102.83	5.481%	$108.4661	$108.47	$108.45	$108.50
Purchase #2	$70.51	11.222%	$78.4226	$78.42	$78.40	$78.40
Purchase #3	$75.42	6.475%	$80.3034	$80.30	$80.30	$80.30
Purchase #4	$182.27	3.284%	$188.2557	$188.26	$188.25	$188.30
Purchase #5	$98.63	12.855%	$111.3089	$111.31	$111.30	$111.30
Purchase #6	$228.51	6.655%	$243.7173	$243.72	$243.70	$243.70
Purchase #7	$146.58	3.289%	$151.401	$151.40	$151.40	$151.40
7 purchase totals =	$904.75		$961.8750	$961.88	$961.80	$961.90