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	$38.54	10.735%	$42.6773	$42.68	$42.70	$42.70
Purchase #2	$42.51	7.815%	$45.8322	$45.83	$45.85	$45.80
Purchase #3	$50.44	3.223%	$52.0657	$52.07	$52.05	$52.10
Purchase #4	$225.82	12.428%	$253.8849	$253.88	$253.90	$253.90
Purchase #5	$61.40	3.740%	$63.6964	$63.70	$63.70	$63.70
Purchase #6	$98.66	6.209%	$104.7858	$104.79	$104.80	$104.80
Purchase #7	$249.52	4.705%	$261.2599	$261.26	$261.25	$261.30
7 purchase totals =	$766.89		$824.2022	$824.21	$824.25	$824.30