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	$103.47	5.430%	$109.0884	$109.09	$109.10	$109.10
Purchase #2	$250.81	9.170%	$273.8093	$273.81	$273.80	$273.80
Purchase #3	$171.72	10.222%	$189.2732	$189.27	$189.25	$189.30
Purchase #4	$63.66	4.752%	$66.6851	$66.69	$66.70	$66.70
Purchase #5	$141.25	10.824%	$156.5389	$156.54	$156.55	$156.50
Purchase #6	$69.30	10.647%	$76.6784	$76.68	$76.70	$76.70
Purchase #7	$82.33	8.124%	$89.0185	$89.02	$89.00	$89.00
7 purchase totals =	$882.54		$961.0918	$961.10	$961.10	$961.10