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	$107.96	13.377%	$122.4018	$122.40	$122.40	$122.40
Purchase #2	$196.90	13.713%	$223.9009	$223.90	$223.90	$223.90
Purchase #3	$238.93	7.415%	$256.6467	$256.65	$256.65	$256.60
Purchase #4	$109.81	13.199%	$124.3038	$124.30	$124.30	$124.30
Purchase #5	$57.45	6.837%	$61.3779	$61.38	$61.40	$61.40
Purchase #6	$20.33	7.759%	$21.9074	$21.91	$21.90	$21.90
Purchase #7	$67.28	8.596%	$73.0634	$73.06	$73.05	$73.10
7 purchase totals =	$798.66		$883.6019	$883.60	$883.60	$883.60