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	$78.48	3.616%	$81.3178	$81.32	$81.30	$81.30
Purchase #2	$228.90	9.817%	$251.3711	$251.37	$251.35	$251.40
Purchase #3	$176.67	5.739%	$186.8091	$186.81	$186.80	$186.80
Purchase #4	$196.66	3.765%	$204.0642	$204.06	$204.05	$204.10
Purchase #5	$72.52	8.687%	$78.8198	$78.82	$78.80	$78.80
Purchase #6	$195.26	8.279%	$211.4256	$211.43	$211.45	$211.40
Purchase #7	$122.74	6.782%	$131.0642	$131.06	$131.05	$131.10
7 purchase totals =	$1,071.23		$1,144.8718	$1,144.87	$1,144.80	$1,144.90